Medical officials in Yemen say security forces killed at least 27 people in the capital Monday, as clashes with anti-government protesters escalated into a military confrontation between government troops and forces loyal to a general who defected to the protesters' side months ago.

Medics say at least one child was killed by sniper fire as government forces fought with troops siding with General Ali Mohsen al Ahmar. Pro-government snipers fired from rooftops in the center of Sana'a, while troops clashed with protesters in another part of the city.

The violence began Sunday when security forces fired on tens of thousands of protesters marching toward the presidential palace from nearby Change Square. Protesters have been camped there for months demanding President Ali Abdullah Saleh step down.

The two-day toll in Sana'a is at least 53 dead and hundreds wounded.

The government said Monday it expresses “sorrow and condemnation” for acts of violence such as those that took place in the capital on Sunday.

Foreign Minister Abu Bakr al-Kurbi told the U.N. Human Rights Council the government will investigate and hold accountable those responsible for the violence.

The youth-led protest movement in Yemen has stepped up demonstrations in the past week, angry after Mr. Saleh instructed his deputy to negotiate a power-sharing deal. Many call the move the latest of the president's delaying tactics.

Mr. Saleh remains in Saudi Arabia, where he has been recovering from injuries sustained in a June attack on his presidential compound.

In April, the six-nation Gulf Cooperation Council proposed a plan designed to end Yemen's turmoil. Mr. Saleh agreed to the proposal three times, but backed out each time before the deal could be signed.