Sanaa , Yemen ( CNN ) -- A violent crackdown by Yemeni authorities has left dozens dead at protests , witnesses and medical officials said Monday . Bloody violence raged Monday in the capital , Sanaa , triggering a new wave of international pressure on Yemen . The United States and the United Nations called for an end to the violence . An official with the human rights group Amnesty International said Yemen is on a `` knife edge '' and the situation could spiral into a civil war . Officials from the United Nations and the Gulf Cooperation Council were in Sanaa , hoping to help organize a peaceful transfer of power . Thirty-one people were killed Monday in clashes in Yemen , 28 in Sanaa , and three in Taiz , according to medical officials . On Sunday , at least 26 protesters were killed and more than 550 were wounded -- hundreds of them by gunshots -- when security forces fired live bullets and tear gas at a massive demonstration in the city , a medic said . The death toll was expected to rise because some were in critical condition , witnesses said . `` The situation is getting very tense , '' said a resident of downtown Sanaa who asked not to be named for safety reasons . `` We can hear gunshots , explosions , RPGs ( rocket-propelled grenades ) constantly . '' `` This now seems more like a military fight , and we 're really worried this could become a civil war . We 're really worried it could spread all over , '' the resident said . The U.S. Embassy in Yemen issued a statement saying the United States `` regrets the deaths and injuries of many people '' in the protests Sunday . `` In this tense situation , we call upon all parties to exercise restraint . In particular , we call on the parties to refrain from actions that provoke further violence . '' The U.S. government remains hopeful for a peaceful transition , the statement said . U.N. Secretary-General Ban Ki-moon 's office said he is `` gravely concerned '' and `` calls on all sides to exercise utmost restraint and desist from provocative actions . He strongly condemns the excessive use of force by government security forces against unarmed protestors in the capital Sanaa , resulting in scores of people killed and many more injured . '' `` Yemen is on a knife edge , '' Philip Luther , Amnesty International 's deputy director for the Middle East and North Africa , said in a statement issued Monday . `` Those who have been protesting peacefully for change are increasingly frustrated by the political deadlock . Meanwhile , eruptions of violence point to a growing risk of civil war . The Yemeni authorities must stop the use of excessive force before the violence spirals out of control . '' The Yemeni government has repeatedly denied accusations of excessive use of force , and said the government is committed to establishing a peaceful transfer of power . Yemeni officials have said forces cracked down on those committing acts of violence during protests . State-run Saba News Agency said Monday that `` militias , armed gangs of the Muslim brotherhood , and the Al Ahamar gang and al Qaeda snipers '' had attacked parts of the capital , even hospitals . `` The attack on security personnel and civilians continued Monday , resulting in casualties , '' Saba reported . Amnesty International said that since February , 200 people have been killed and more than 1,000 have been injured in protests in Yemen `` as security forces have repeatedly used excessive force , including by firing live ammunition at peacefully gathered protesters . '' A video on YouTube Monday purports to show the body of a 10-month-old child killed by gunmen in Sanaa . According to a medical team in Change Square , the baby was inside his father 's vehicle when a stray bullet hit him in the middle of the forehead . U.N. envoy to Yemen Jamal Benomar and Gulf Cooperation Council Secretary General Abdul Latif al-Zayyani arrived in Yemen on Monday , Saba reported . They will be discussing a GCC proposal for transferring power , the agency said . The proposal , backed by the six Arab nations that make up the council , was put forward in May . It would allow Yemen 's embattled President Ali Abdullah Saleh to transfer his executive powers to Vice President Abd Rabo Mansou Hadi within 30 days . According to the proposal , Saleh would then formally resign . Saleh initially indicated he would go along with it , but then refused to sign . The ongoing violence is stepping up pressure for a transition . On Monday , troops were seen shooting randomly at protesters as demonstrations continued throughout the capital on almost every street , witnesses said . All roads leading to Change Square , where thousands have been conducting a seven-month sit-in to call for the resignation of Saleh , remained closed Monday . Saleh , who is recuperating in Saudi Arabia from a June attack on his palace , has vowed to return to Yemen to finish his term . The state-run Saudi Press Agency said Saudi King Abdullah met Monday with Saleh , who expressed gratitude for the medical care . The king wished `` all our brothers in Yemen will overcome the current crisis , '' SPA reported . The uprising in Yemen is part of the so-called Arab Spring , in which protesters seeking political reforms have taken to the streets in many countries throughout the Middle East and North Africa . CNN 's Mohammed Jamjoom and journalist Hakim Almasmari contributed to this report .
The Yemeni government says gangs and al Qaeda snipers attacked the capital . `` We 're really worried this could become a civil war , '' a resident says . The U.N. secretary-general condemns `` excessive use of force '' by Yemen . In Yemen, where President Ali Abdullah Saleh has been in power for 33 years, there are fears that his regime is on its last legs as he struggles to hold onto power.