(Adds public announcement and Foreign Ministry statement)
* Protesters back out after two killed in Mandalay
* Towns across the country see peaceful protests
* U.S. 'deeply concerned' by violence
* Foreign Ministry says authorities exercising utmostrestraint
* Facebook removes main military page for inciting violence
Feb 21 (Reuters) - Huge crowds marched in Myanmar on Sundayto denounce a Feb. 1 military coup in a show of defiance afterthe bloodiest episode of the campaign for democracy the previousday, when security forces fired on protesters, killing two.
The military has been unable to quell the demonstrations anda civil disobedience campaign of strikes against the coup andthe detention of elected leader Aung San Suu Kyi and others,even with a promise of new elections and stern warnings againstdissent.
Tens of thousands of people massed peacefully in the secondcity of Mandalay, where Saturday's killings took place,witnesses said.
"They aimed at the heads of unarmed civilians. They aimed atour future," a young protester told the crowd.
The Foreign Ministry said in a statement that despite"unlawful demonstrations, incitements of unrest and violence,the authorities concerned are exercising utmost restraintthrough minimum use of force to address the disturbances",adding they were maintaining public safety in line with domesticlaws and international practices.
In the main city of Yangon, thousands of mostly young peoplegathered at different sites to chant slogans and sing.
"Us young people have our dreams but this military coup hascreated so many obstacles," said Ko Pay in Yangon. "That's whywe come out to the front of the protests."
In Myitkyina in the north, people laid flowers for the deadprotesters. Big crowds marched in the central towns of Monywaand Bagan, in Dawei and Myeik in the south, Myawaddy in the eastand Lashio in the northeast, posted pictures showed.
At the tourist spot of Inle Lake, people including Buddhistmonks took to a flotilla of boats holding aloft portraits of SuuKyi and signs saying "military coup - end".
The more than two weeks of protests had been largelypeaceful until Saturday, unlike previous episodes of oppositionduring nearly half a century of direct military rule to 2011.
The violence looked unlikely to end the agitation.
"The number of people will increase ... We won't stop,"protester Yin Nyein Hmway said in Yangon.
Several Western countries that have condemned the coupdecried the violence against protesters.
U.S. State Department spokesman Ned Price said the UnitedStates was "deeply concerned". France, Singapore, Britain andGermany also condemned the violence and U.N. Secretary-GeneralAntonio Guterres said lethal force was unacceptable.
Sunday's Foreign Ministry statement reiterated the junta'sstance that the takeover was constitutional and said remarks bysome embassies and foreign countries "are tantamount to flagrantinterference in internal affairs of Myanmar".
Military spokesman Zaw Min Tun has not responded toattempts by Reuters to contact him by telephone for comment.
The trouble in Mandalay began with confrontations betweenthe security forces and striking shipyard workers.
Video clips on social media showed members of the securityforces firing at protesters and witnesses said they found thespent cartridges of live rounds.
U.N. Special Rapporteur for Myanmar Tom Andrews said he washorrified by the deaths of the two, one of them a teenaged boy.
"From water cannons to rubber bullets to tear gas and nowhardened troops firing point blank at peaceful protesters. Thismadness must end, now," he said on Twitter.
The state-run Global New Light of Myanmar newspaper said thestrikers sabotaged boats at the city's river port and attackedpolice with sticks, knives and catapults. Eight policemen andseveral soldiers were injured, it said.
"Some of the aggressive protesters were also injured due tothe security measures conducted by the security force inaccordance with the law," the newspaper said without mentioningthe deaths.
Suu Kyi's National League for Democracy (NLD) called theviolence by security forces in Mandalay a crime againsthumanity.
In an announcement on state-owned media MRTV late on Sunday,authorities said that by planning a big demonstration on Monday,protesters were inciting anarchy and pushing young peopletowards a path of confrontation "where they will suffer the lossof life".
FUNERAL FOR PROTESTER
A young woman protester, Mya Thwate Thwate Khaing, becamethe first death among the demonstrators on Friday. She was shotin the head on Feb. 9 in the capital Naypyitaw.
Hundreds of people attended her funeral on Sunday.
Military media said the bullet that killed her did not comefrom any gun used by police and so must have been fired by an"external weapon".
The army says one policeman has died of injuries sustainedin a protest.
The army seized power after alleging fraud in Nov. 8elections that the NLD swept, detaining Suu Kyi and others. Theelectoral commission dismissed the fraud complaints.
Facebook deleted the military's main page forrepeated violations of its standards "prohibiting incitement ofviolence and coordinating harm".
A rights group said 569 people have been detained inconnection with the coup.(Reporting by Reuters staff; Writing by Robert Birsel andFrances Kerry; Editing by William Mallard, Lincoln Feast andEdmund Blair)