The United Nations said Wednesday that Ethiopia had detained 72 aid drivers to the conflict-torn north, the latest roundups despite an international push to end a brutal war.

The news, which came a day after the UN reported the arrests of employees in the capital Addis Ababa, is likely to further inflame tensions with the government following a decision in September to expel seven senior UN officials for "meddling" in the country's affairs.

A UN spokesperson said the latest detentions targeted contract drivers for the World Food Programme (WFP) in the capital of Afar province, on the only functional road leading into famine-threatened Tigray.

"We confirm that 72 outsourced drivers contracted by WFP have been detained in Semera. We are liaising with the government of Ethiopia to understand the reasons behind their detention," a UN spokesperson said. 

At the world body's headquarters, UN spokesman Stephane Dujarric said, "We are calling for their release."

He said that at least nine UN staff members also remained in custody in Addis Ababa, a day after saying that 22 had been rounded up.

Officials last week announced a six-month nationwide emergency amid rising fears that fighters from the Tigray People's Liberation Front (TPLF) and Oromo Liberation Army (OLA) rebel groups could advance on the capital.

Lawyers say arbitrary detentions of ethnic Tigrayans -- commonplace during the war -- have surged since then, ensnaring thousands, with the new measures allowing the authorities to hold anyone suspected of supporting "terrorist groups" without a warrant. 

Law enforcement officials describe such detentions as part of a legitimate crackdown on the TPLF and OLA. 

Information on the ethnicity of the drivers detained in Semera was not immediately available, though the UN has in the past hired ethnic Tigrayans to transport food and other aid into Tigray.

- Famine fears -
Prime Minister Abiy Ahmed sent troops into Tigray last November to topple the TPLF, a move he said came in response to rebel attacks on army camps.

Though the 2019 Nobel Peace laureate vowed a swift victory, by late June the TPLF had retaken most of the region including its capital Mekele.

Since then Tigray has been under what the UN describes as a de-facto humanitarian blockade.

Only 15 percent of necessary aid has been able to cross from Semera into Tigray since mid-July, with hundreds of thousands of people living in famine-like conditions, according to UN estimates.

Foreign envoys are scrambling to end the war and mitigate further suffering, putting hope in a push of the African Union led by former Nigerian president Olusegun Obasanjo.

"I believe that all sides see the dangers of perpetuating the conflict," US Secretary of State Antony Blinken told reporters in Washington.

"We are hopeful that, given the important work that president Obasanjo is engaged in -- the efforts that we're making and others are engaged in -- that there is still a window to pull back and to move this to a better place," he said.

The US secretary of state also spoke with his Ethiopian counterpart Demeke Mekonnen, with whom he stressed "the urgency of taking concrete steps for peace."

But TPLF spokesman Getachew Reda appeared to dismiss peace initiatives Wednesday, saying on Twitter that they seemed "mainly about saving #Abiy".

- Mass rape claims -
The fighting has extracted a huge humanitarian toll, with rights groups on Wednesday issuing new reports on sexual violence in the war.

Human Rights Watch said the Abiy government's "effective siege" of Tigray -- where Ethiopian and Eritrean soldiers are accused of mass rapes -- was preventing survivors from getting health care and other critical services.

Amnesty International said Tigrayan rebels had raped, robbed and beat up women during an attack on a town in Amhara region, south of Tigray.

In a statement, the TPLF criticised Amnesty's "disturbingly flawed methodology."

"(The report) seems to have arrived at its sweeping conclusions based on the results of remote interviews with the alleged victims," it said.

"If our investigation discovers that Tigrayan fighters have in fact committed such crimes, the government of Tigray will bring the perpetrators to justice."

The Ethiopian government's communication service said in a statement that the atrocities "committed by the terrorist TPLF should be condemned by all" and claimed there were "even more inhumane actions being committed in the territories it currently occupies."