Suu Kyi, 76, has been detained since the February 1 coup last year that triggered mass protests and a crackdown on dissent with more than 1,500 civilians killed, according to a local monitoring group.

The military junta has now charged her with influencing election officials during 2020 polls, a source said, on top of previous charges, including violating the country's official secrets laws.

If convicted of all charges, the Nobel laureate could face sentences tallying more than 100 years in prison.

Ahead of the Tuesday anniversary of the putsch, the junta warned that holding protests or sharing "propaganda" against the military could lead to charges under the anti-terrorism law.

The United States marked one year since the coup by placing sanctions on Attorney General Thida Oo, Supreme Court Chief Justice Tun Tun Oo and Anti-Corruption Commission chairman Tin Oo, whom it said were closely involved in the "politically motivated" prosecution of Suu Kyi.

"We are coordinating these actions with the United Kingdom and Canada... to further promote accountability for the coup and the violence perpetrated by the regime," US Secretary of State Antony Blinken said.

"The United States will continue... to address human rights abuses and press the regime to cease the violence, release all those unjustly detained, allow unhindered humanitarian access, and restore Burma's path to democracy," he added, using Myanmar's former name.

The junta canceled the results of the 2020 election in July last year, saying it had found some 11.3 million instances of fraud.

Independent monitors said the polls were largely free and fair.

The junta has promised to hold another election by August 2023 if stability in the country -- currently riven by fighting between the military and anti-coup fighters -- is restored.

- Another trial for Suu Kyi -

Suu Kyi has already been sentenced to six years in jail for illegally importing and owning walkie talkies, incitement against the military and breaking Covid-19 rules.

She will face a further trial on charges of influencing the country's election commission during the 2020 polls that saw her National League for Democracy (NLD) party defeat a military-aligned rival, a source with knowledge of the case said.

The case is expected to be wrapped up within six months. Former president and NLD stalwart Win Myint will face the same charge.

Several senior members of the electoral commission have also been arrested since the coup, accused of masterminding the NLD's landslide victory.

On Monday, ousted Myanmar lawmakers from a shadow "National Unity Government" addressed the media in Paris.

Human rights spokesman Aung Myo Min urged the international community to implement an arms embargo and tighten economic sanctions to cut off all trade with the regime.

Following the US lead, Britain said it was imposing sanctions against Thida Oo, Tin Oo and a third person, the chair of the country's election commission.

"The Burmese military are using ever more brutal and desperate tactics to try to cling on to power," said Anna Roberts, head of Burma Campaign UK, welcoming the fresh sanctions.

"The British government is doing exactly the right thing... however, they need to speed up the pace of new sanctions. It is vital to maximise pressure now while the military are more vulnerable."

The Canadian government imposed similar new sanctions, saying the military regime had "shown no sign of reversing course" over the past year.