Cairo (CNN) -- At least 38 people, including six children, were killed Thursday by security forces across Syria, a network of opposition activists said.
In the besieged western city of Homs, the 16 fatalities included an infant who died at Al-Bir Hospital, the Local Coordination Committee of Syria said. The child, who was bleeding in the colon, died after security forces prevented the transfer of blood to the hospital, they said.
Activist Mahmud Tayyara was killed by a bullet to his head fired at a checkpoint in Homs' Me'zanatain neighborhood, the committee said.
Ten people were killed in Idlib, six in Hama, three in the suburbs of Damascus and three in Daraa, said the LCC, which organizes and documents anti-government demonstrations.
The bodies of three young men who had been riding in a taxi that was stopped by security cars were found Thursday in Hama, the organization said.
CNN could not confirm the accounts, since the Syrian government has limited access to the country by international reporters.
The London-based Syrian Observatory for Human Rights said that military reinforcements have arrived at the entrances to the city of Khan Chikhoun in Idlib province, where more than 17 members of the Syrian army and security forces had been killed and dozens wounded since Thursday afternoon. The fighting was believed to be between the government security forces and army defectors, the group said.
"It has been confirmed that 15 soldiers have defected from the army in the same area Thursday night" after the clashes began, the opposition group said. The army and the security forces have withdrawn from most government and security buildings in the city as well as from a main health clinic, it added.
Witnesses said explosions erupted in parts of the city into the night.
The state-run Syrian Arab News Agency said two children from al-Moallaqa village in the northern province of Idlib were killed Thursday "after explosives hidden by a terrorist armed group in an abandoned house blasted in the village."
It added that two members of the government security forces died and two army members were wounded "by a terrorist armed group" in the village al-Kfair village in Jisr al-Shugur.
As the government crackdown continued, Amnesty International urged the the Arab League to press Damascus to allow independent human rights monitors into the country.
President Bashar al-Assad had promised to abide by an Arab League proposal to halt all violence, release all detainees, withdraw all armed elements from populated areas and allow unfettered access to the nation by journalists and Arab League monitors.
But since that agreement, Amnesty International said, more than 100 people are reported to have been killed. The human rights monitor said most of the dead appear to have been unarmed protesters and bystanders who were shot by the security forces and army.
"Killings and arrests of unarmed protesters and others continue to be reported on a daily basis, making a mockery of Syria's promises to the Arab League," said Philip Luther, Amnesty International's acting director for the Middle East and North Africa.
Amnesty International wrote Thursday to the Arab League, asking it to secure access to Syria for Amnesty International staff as well as those of the U.N. Office of the High Commissioner for Human Rights.
More than 3,500 Syrians have been killed since the government crackdown on protesters started in mid-March, the United Nations High Commissioner for Human Rights estimated.
CNN's Kamal Ghattas contributed to this story from Atlanta.