Gunfire and shelling was heard early Tuesday in the Yemeni capital Saana, as violence continued for a third day.

A further two protesters were reportedly shot dead by security forces, bringing the death toll to 55 since Sunday.

Agence France Presse reported that two children shot dead by snipers were among 27 people killed on Monday.

Witnesses said troops of dissident General Ali Mohsen al-Ahmar were clashing with those loyal to President Ali Abdullah Saleh.

The BBC said the violence is the worst Yemen has seen for several months. It reported witness accounts that government troops were shooting protesters from the rooftops in Saana.

The violence coincided with the arrival of the United Nations envoy to Yemen, Jamal Benomar, and Gulf Cooperation Council chief Abdullatif al-Zayani.

Meanwhile the charity Oxfam said one in three Yemenis is suffering from hunger as a result of the political stalemate.

According to a report published Monday, a sharp rise in food and water prices has left a third of Yemen's 22 million people going hungry.

But despite the violence in the country, Oxfam spokesman, Richard Stanforth, said the organization could work safely in Yemen.