( CNN ) -- A small group of observers resumed the United Nations ' mission to monitor a truce in Syria that was tenuous from the start and showed signs Wednesday of unraveling as opposition activists again reported widespread violence . In what appeared to be a pattern of retaliation , security forces were accused of attacking a number of hot spots , including the cities of Hama and Douma , after U.N. monitors had left the areas . Security forces have also reportedly targeted residents who have spoken to the monitors , according to Ahmad Fawzi , spokesman for special envoy Kofi Annan . Fawzi told the U.N. Security Council that people have been harassed and even killed for speaking with the monitors . One activist in Douma urged the monitors to return to the besieged city to see what was unfolding in the wake of their departure . `` The security forces have continued their siege on Douma for the second day today , '' said Mohammed , identified only by his first name for safety reasons . `` We desperately call on the international monitors to return to Douma to see the other face of the regime , '' he said . In remarks to the Security Council on Tuesday , Annan criticized reports of actions forces loyal to President Bashar al-Assad . `` I am particularly alarmed by reports that government troops entered Hama ( Monday ) after observers departed , firing automatic weapons and killing a significant number of people , '' Annan said . `` If confirmed , this is totally unacceptable and reprehensible . '' Violence erupted again nationwide Wednesday . At least 100 people were killed , including 70 in Hama , 16 of whom were children , said the opposition Local Coordination Committees of Syria . The reported violence in the southern city of Hama occurred two days after a visit to the city by U.N. observers . An activist in Hama told CNN that at least 56 people were killed in the shelling of the city 's Masha Tayar neighborhood on Wednesday . The activist said that the Syrian military began shelling the neighborhood at noon ( 5 a.m . ET ) , causing a number of houses to collapse , killing those inside . The LCC said residents were still pulling bodies from the rubble late in the evening . CNN can not independently verify reports of violence and deaths within Syria , as the government has restricted access by international media . A handful of U.N. observers have in recent days toured restive cities and towns after Annan , the joint U.N.-Arab League envoy , brokered a six-point peace plan with al-Assad . Annan said Syria 's foreign minister told him that heavy weapons and troops had been withdrawn from population centers and that military operations had ended , key elements of the peace plan . Annan described the communication as `` encouraging , '' but added , `` the only promises that count are the promises that are kept . '' U.S. Sen. John McCain , R-Arizona , told CNN that he had little hope for success for the United Nations mission in Syria . `` How atrocious is it that the government allows these monitors in , people have the courage to come out and express their grievances and then they slaughter people , '' he said . `` If it was n't so serious , it would be a bad joke . '' The ongoing carnage , say opposition activists , is proof that al-Assad does not intend to keep his promises . At least 38 people were killed across the country Tuesday , the LCC said . The Red Cross said Mohammed al-Khadraa , a Syrian Arab Red Crescent volunteer , was killed and three others were injured in Douma on Tuesday evening . Al-Khadraa was shot and killed in a vehicle clearly marked with the Red Crescent emblem , the agency said . The U.N. Security Council recently authorized sending up to 300 monitors to Syria for 90 days . They are tasked with observing a cease-fire that was supposed to have begun April 12 . By next Monday , 30 observers are expected to be on the ground , with that number swelling to 100 by month 's end . But as of Wednesday , only 13 were in Syria . One problem is that Damascus is unwilling to allow monitors from any of the 60-plus nations that are part of the `` Friends of Syria , '' a group that aims to find a solution to the crisis . The group , which includes the United States , France and Britain , met this month and recognized the opposition Syrian National Council as a legitimate representative of the Syrian people . Analysis : U.N. mission does nothing to change endgame in Syria . Nationalities aside , some question whether the observers will be able to get an objective , comprehensive view of the situation . `` They are all the time watched by the security forces of the regime , '' said one opposition activist , who is not being identified for safety reasons . The observers are also tasked with implementing the peace plan , which calls for the government and the opposition to end the bloodshed , provide access to the population for humanitarian groups , release detainees and start a political dialogue . The crisis began in March 2011 , when the government started cracking down on peaceful protesters calling for the ouster of al- Assad , whose family has ruled Syria for 42 years . The United Nations estimates at least 9,000 people have since died , while activist groups put the death toll at more than 11,000 . CNN 's Yousuf Basil , Amir Ahmed , Holly Yan , Moni Basu , Joe Vaccarello , Jill Dougherty and Elizabeth Joseph contributed to this report .
NEW : Shelling in Hama causes a number of buildings to collapse , witness reports . They say fresh violence continues in Douma and Hama after U.N. monitors leave . Syria is not killing monitors from Friends of Arab nations , a U.N. official says . Hillary Clinton : It is ` ` absolutely deplorable '' if the government is killing those who spoke to monitors .