At least nine people have been killed in Yemen's capital, Sana'a, where security forces have been clashing with dissident troops and protesters.

It is the third straight day of violence in the capital. More than 60 people have been killed since Sunday.

Witnesses say machine gun fire and heavy shelling rocked Sana'a Tuesday, with some shells falling on an anti-government protest camp called Change Square.

Officials say those killed include three soldiers loyal to Ali Mohsen al-Ahmar, a general who defected to the opposition months ago. Since he defected, Sana'a has been split between the breakaway troops and government forces.

Yemen's youth-led protest movement stepped up demonstrations last week, angry after President Ali Abdallah Saleh instructed his deputy to negotiate a power-sharing deal. Many called the move the latest of the president's delaying tactics as he avoids demands to step down.

Diplomats and Yemeni politicians are trying to revive a long-stalled transition plan under which Mr. Saleh would hand over power. U.N. envoy Jamal bin Omar and the secretary-general of the six-nation Gulf Cooperation Council arrived in Sana'a Monday and were expected to join the talks.

Mr. Saleh has agreed to the GCC proposal three times since April. However, in each case, he backed out before a deal could be signed.

Meanwhile, the International Organization for Migration says Yemen's violence over the past few days has complicated efforts to evacuate several thousand mostly Ethiopian migrants who are stranded near the Saudi border with Yemen.