* Suu Kyi video court hearing due amid report of treason charge
* At least 536 civilians killed since coup - activist group
* UN envoy to Myanmar warns risk of 'imminent bloodbath'
* US urges China to use influence to hold junta accountable
* China foreign minister meets Southeast Asian counterparts
Myanmar activists burned copies of a military-framed constitution on Thursday two months after the junta seized power, as a U.N. special envoy warned of the risk of a bloodbath because of an intensified crackdown on anti-coup protesters.
Myanmar has been rocked by protests since the army overthrew the elected government of Nobel laureate Aung San Suu Kyi on Feb. 1 citing unsubstantiated claims of fraud in a November election.
Suu Kyi and other members of her National League for Democracy (NLD) have been detained.
The junta has accused her of several minor crimes including illegally importing six handheld radios and breaching coronavirus protocols but a domestic media outlet reported on Wednesday she could be charged with treason, which can be punishable by death.
But one of her lawyers, Min Min Soe, said no new charges were announced at a hearing in her case on Thursday.
Her lawyers have said the charges she faces were trumped up.
The UN envoy's warning of a bloodbath follows a flare-up in fighting between the army and ethnic minority insurgents in frontier regions.
At least 20 soldiers were killed and four military trucks destroyed in clashes with the Kachin Independence Army (KIA), one of Myanmar's most powerful rebel groups, DVB news reported.
Reuters could not immediately verify the reports and a junta spokesman did not answers calls seeking comment.
Myanmar military aircraft have started bombing positions of another group, the Karen National Union (KNU), for the first time in more than 20 years and thousands of villagers have fled from their homes, many into Thailand.
In cities across Myanmar there were candle-lit protests overnight and marches at dawn on Thursday, according to media and photographs on social media.
Protests gathered in several places on Thursday and two people were wounded when police opened fire in the central town of Monywa, according to witnesses posts on social media.
The coup has led to new calls for unity among those opposed to military rule, in particular city-based democracy campaigners and ethnic minority forces battling in frontier regions.
Ousted members of parliament, mostly from Suu Kyi's party, have vowed to set up a federal democracy in a bid to address a long-standing demand from minority groups for autonomy.
They also announced the scrapping of a 2008 constitution drawn up by the military that enshrines its control over politics. The military has long rejected the idea of a federal system, seeing itself as the central power vital to holding the fractious country together.
Social media posts showed copies of the constitution, real and symbolic, being burned at rallies and in homes during what one activist called a "constitution bonfire ceremony".
"The new day begin here!" Dr Sasa, the international envoy for the ousted parliamentarians said on Twitter, referring to what for now is a largely symbolic move.
SOUTHEAST ASIAN MINISTER IN CHINA
The U.N. special envoy on Myanmar, Christine Schraner Burgene, told the 15-member U.N. Security Council that the military was not capable of managing the country, and warned the situation on the ground would worsen.
The council must consider "potentially significant action" to reverse the course of events as "a bloodbath is imminent", she said.
The council has expressed concern and condemned violence against protesters, but dropped language calling the takeover a coup and threatening possible further action due to opposition by China, Russia, India and Vietnam.
At least 536 civilians have been killed in protests, 141 of them on Saturday, the bloodiest day of the unrest, according to the Assistance Association for Political Prisoners (AAPP).
The United States on Wednesday urged China, which has significant economic and strategic interests in Myanmar, to use its influence to hold to account those responsible for the coup.
While Western countries have condemned the coup, China has been more cautious and the government's top diplomat Wang Yi called for stability during a meeting with his Singaporean counterpart on Wednesday.
Wang said China welcomed and supported a long-standing principle of the Association of Southeast Asian Nations (ASEAN) of not interfering in each other's internal affairs, even though there have been signs in recent weeks that adherence to the principle is wearing thin.
Indonesia, Singapore, Malaysia and the Philippines have all spoken out about the situation in Myanmar and Thailand issued its strongest comments on Thursday, saying it was "gravely troubled" by the violence and calling for an end to it and the release of detainees.
In a sign of stepped-up shuttle diplomacy, the foreign ministers of Malaysia, Indonesia and the Philippines are due to meet Wang in China this week
The Myanmar military has traditionally been impervious to external pressure.