US President Joe Biden met Wednesday with the parents of a former US Marine imprisoned in Russia and promised to work to end the "nightmare" of his detention, the White House said.

US citizen Trevor Reed is serving a nine-year prison term in a penal colony some 500 kilometers (300 miles) southeast of Moscow after being convicted of assaulting police officers while drunk in 2019.

"President Biden met today with Joey and Paula Reed, the parents of Trevor Reed, who is wrongfully detained in Russia," presidential spokeswoman Jen Psaki said in a statement.

"During their meeting, the President reiterated his commitment to continue to work to secure the release of Trevor, Paul Whelan, and other Americans wrongfully held in Russia and elsewhere."

"We understand the pain felt by all of Trevor's families and friends enduring the nightmare of his absence, which we are committed to bringing to an end."

A spokesman for Reed said Tuesday that the ex-Marine was "back on hunger strike and back in solitary," according to a statement posted on Twitter.

Reed had announced a hunger strike on November 4, which lasted for two weeks, saying he had been repeatedly placed in an isolation cell for allegedly breaking prison rules.

He denied any wrongdoing.

Diplomatic tensions between Washington and Moscow have soared since Russia invaded Ukraine.

US State department spokesman Ned Price said that US diplomats are being denied access to Americans being held by Russia.

Those include Reed and Paul Whelan, who are being held on what the United States says are false or trumped-up charges.

Another American held is professional basketball Brittney Griner, who was detained in Moscow airport on February 17 on charges of carrying vape cartridges that contained cannabis oil in her luggage.

Washington fears she will be used as a pawn in the Ukraine dispute and has so far kept a low profile in her case.

UK spy chief 

Russian President Vladimir Putin's advisors fear telling him the truth about his "failing" Ukraine war strategy, the head of Britain's top communications spying agency said Thursday.

Putin had "massively misjudged" the invasion, the director of Britain's intelligence agency GCHQ Jeremy Fleming said in a prepared speech to the Australian National University in Canberra.

His remarks, released in advance, echoed US intelligence issued by the White House the previous day indicating Putin was being "misinformed" by his advisors about the progress of the Russian operation.

Western intelligence sources have been keen to play up Russia's failures in the war and highlight divisions within Putin's inner circle. 

Fleming said Putin had underestimated the Ukraine resistance, the strength of the international coalition against him, and the impact of economic sanctions.

The Russian leader had also overestimated his own military's ability to secure a rapid victory, he added.

"We've seen Russian soldiers -- short of weapons and morale -- refusing to carry out orders, sabotaging their own equipment and even accidentally shooting down their own aircraft," Fleming said.

"And even though Putin's advisors are afraid to tell him the truth, what's going on and the extent of these misjudgements must be crystal clear to the regime."

Russia's public statement this week that it would "radically" reduce combat operations around the capital Kyiv and the northern city of Chernigiv "perhaps shows they have been forced to significantly rethink", Fleming said.

He warned that cyber attacks from Russia remain a threat.

Though some people were surprised that Moscow had not launched a catastrophic cyber attack, Fleming said it was "never our understanding" that such an offensive was central to the Russian invasion.

Britain's intelligence services had, however, detected a "sustained intent from Russia to disrupt Ukrainian government and military systems", he said.

"We've certainly seen indicators which suggests Russia's cyber actors are looking for targets in the countries that oppose their actions."

On the battlefields in Ukraine, Moscow was using mercenaries and foreign fighters to support its own forces, Fleming said.

They included the Wagner Group, which was "taking it up a gear" after being active in the country since the Russian annexation of Crimea in 2014.

"The group works as a shadow branch of the Russian military, providing implausible deniability for riskier operations," he said.

Fleming noted that Chinese President Xi Jinping had refused to condemn the invasion, providing a level of diplomatic and economic support for Russia.

"With an eye on re-taking Taiwan, China does not want to do anything which may constrain its ability to move in the future," he said, predicting however that the China-Russia relationship may deteriorate as China's military and economy grow in power.

Latest developments
Here are the latest developments in the war in Ukraine: 

- Putin misled on Ukraine: US, UK -
British intelligence says advisors to Russia's President Vladimir Putin fear telling him the truth about his "failing" and "massively misjudged" invasion of Ukraine.

US officials meanwhile say Putin feels "misled" by his military on war's progress and the impact of sanctions, saying his mistrust in military leadership is causing "persistent tensions".

Western intelligence has been keen to play up Russia's failures in the war and highlight divisions within Putin's inner circle.

- Moscow announces Mariupol ceasefire-
Russia's defence ministry announces a local ceasefire Thursday to allow civilians to be evacuated from Ukraine's besieged port city of Mariupol.

It says a humanitarian corridor will be opened to Zaporizhzhia with cooperation from the UN refugee agency and the International Committee of the Red Cross.

But previous attempts to allow civilians out of the devastated town have failed, and Ukraine's deputy prime minister describes the proposal as "another manipulation."

- Zelensky denies Russian scaleback -
Ukrainian President Volodymyr Zelensky says he does not trust Russian claims it will scale back military activity around the capital Kyiv and another city.

"We don't believe anyone, not a single beautiful phrase," he says in a video address, adding that Russian troops are regrouping to strike the eastern Donbas region. 

- Peace talks downplayed - 
The Kremlin plays down hopes of a breakthrough following Tuesday's peace talks in Istanbul, saying there was nothing "too promising" from the discussions.

France too says there was "no breakthrough or anything new" after the talks, despite Russia's main negotiator having cited progress on Russia's demand for Ukrainian neutrality.

- Shelling despite Russia pledge - 
Authorities in Chernigiv say the area was "shelled all night" despite Russia's pledge to reduce military activity there and in the capital.

AFP reporters also hear frequent explosions coming from the direction of the flashpoint Kyiv suburb of Irpin.

Separately, Ukrainian officials say a Red Cross facility was hit by Russian strikes in Mariupol, though there is no detail on when the attack happened.

- Kyiv suburb 'half destroyed' -
The mayor of Irpin says at least 200 people have been killed and more than half of the town destroyed in the fierce battle to control the western gateway to the capital.

He says that the town, which was retaken by Ukraine from Russian forces this week, is still being shelled.

- Biden, Zelensky talks -
US President Joe Biden and President Volodymyr Zelensky discuss "additional capabilities" to help the Ukrainian military, during a telephone call, the White House says.

- War crimes warning - 
The United Nations human rights chief says that Russia's widespread and indiscriminate attacks in populated areas of Ukraine could amount to "war crimes".

- Russia moving out of Chernobyl: US -
Russian forces have begun to pull out of the defunct Chernobyl nuclear power site and move towards Belarus, a US defence official says.

Troops seized control of the Chernobyl site -- where radioactive waste is still stored -- on February 24, the first day of the invasion.

- Austria, Germany act on gas -
Austria and Germany activate their emergency plans to secure gas supplies, as fears rise that Russia could cut off supplies if Western countries refuse to make payments in rubles.

Putin, however, tells Chancellor Olaf Scholz Germany could continue paying for Russian gas in euros, the Berlin government says.

- Russia-China unity -
Russian Foreign Minister Sergei Lavrov says Russia and China are pursuing a "multipolar, just, democratic" world order on his first visit to Moscow's key ally since the invasion of Ukraine. 

China responds that "China-Russia cooperation has no limits".

Lavrov will this week also visit India, which, like China, has avoided condemning the invasion.

- Four million refugees -
More than four million Ukrainians have fled the country since the start of the war, the UN says.