Myanmar's generals ordered internet providers to restrict access to Facebook Thursday, as UN chief Antonio Guterres said the world must rally to ensure the military coup fails.

The Southeast Asian nation was plunged back into direct military rule on Monday as de facto leader Aung San Suu Kyi and other civilian leaders were detained in a series of dawn raids, ending the country's brief experiment with democracy.

The coup sparked international condemnation and fears the military will drag 54 million people back to the decades of junta rule that turned Myanmar into one of Asia's most impoverished and repressive nations.

With soldiers back on the streets of major cities, the takeover has so far not generated any mass pro-democracy street protests.

However hundreds of supporters of the "Tatmadaw," as the military is called, rallied in the capital Naypyidaw Thursday in support of the coup, waving the red flag of the armed forces.

Some carried signs which read: "National betrayers who depend on foreign countries are not wanted" and "Tatmadaw that loves people... may you be successful."

But people have flocked to social media to voice opposition and share plans for civil disobedience -- especially on Facebook. 

"We have digital power... so we've been using this since day one to oppose the military junta," said activist Thinzar Shunlei Yi, who's behind a so-called "Civil Disobedience Movement" fanning out across social media platforms. 

Telenor, one of the country's main telecoms providers, confirmed Thursday that authorities had ordered it to "temporarily block" Facebook access.

The Norwegian-owned company said it had to comply but "does not believe that the request is based on necessity and proportionality, in accordance with international human rights law".

Facebook confirmed access "is currently disrupted for some people" and urged authorities to restore connectivity. 

NetBlocks, which monitors internet outages around the world, said the disruptions were also affecting Facebook-owned apps such as Instagram and WhatsApp.

For many in Myanmar, Facebook is the gateway to the internet and a vital way to gather information.

"The first thing we look at each morning is our phone, the last thing we look at in the night is our phone," Aye, a 32-year-old entrepreneur opposed to the coup, told AFP.

A small rally kicked off Thursday in front of Mandalay Medicine University, with protesters carrying signs that said "People's protest against the military coup!"

Local media said police arrested four people, although authorities could not confirm the detentions to AFP. 

Meanwhile, 70 MPs from Suu Kyi's National League for Democracy party signed a "pledge to serve the public" while staging their own symbolic parliamentary session in Naypyidaw, according to local media.

Coup must fail

Army chief Min Aung Hlaing's coup has left the international community scrambling to respond.

On Wednesday, UN Secretary-General Guterres said he would pressure the generals to reverse course, in his most forceful comments yet.

"We will do everything we can to mobilise all the key actors and international community to put enough pressure on Myanmar to make sure that this coup fails," Guterres told The Washington Post.

"It's absolutely unacceptable to reverse the results of the elections and the will of the people."

Min Aung Hlaing justified his coup by alleging widespread voter fraud during November's election. 

Suu Kyi, who has not been seen in public since she was detained, won a huge landslide with her NLD, while the military's favoured parties received a drubbing.

International and local observers -- as well as Myanmar's own election monitor -- reported no major issues that might have affected the integrity of the vote.

Myanmar's junta-era constitution ensures the military retains considerable influence, including a quarter of parliamentary seats and control of key ministries.

But analysts say top generals feared their influence was waning and were dismayed by the enduring appeal of Suu Kyi.

On Wednesday authorities brought an obscure charge against the 75-year-old to justify her ongoing detention. 

According to her party, she was charged with an offence under Myanmar's import and export law after authorities found unregistered walkie-talkies at her home.

The United States and Britain condemned the charges and called for her immediate release.

Limited options

Myanmar's military has declared a one-year state of emergency and said it would hold new elections once its allegations were addressed.

That has caused huge anger inside the nation, but opposing the military is fraught with risk. 

During junta rule, dissent was quashed with thousands of activists -- including Suu Kyi -- detained for years on end.

Censorship was pervasive and the military frequently deployed lethal force, most notably during huge protests in 1988 and 2007.

The new government has already issued a warning telling people not to say or post anything that might "encourage riots or an unstable situation".

The UN Security Council met Tuesday but failed to agree on a statement condemning the coup. Diplomats said veto-wielding China and Russia, Myanmar's main supporters at the UN, had asked for more time to finesse the Council's response.