Homs is heavily shelled on the third day of a truce in Syria.

The UN Security Council will send an advance team of observers on Sunday, to start monitoring the delicate ceasefire.

Russia and China joined the rest of the Security Council in authorising the deployment of 30 unarmed observers.

It was the first unanimously approved resolution on Syria since the uprising erupted last year.

The resolution also included a vague warning to Damascus, saying the Council would consider further steps.

A surge in violence has threatened peacekeeping efforts led by Kofi Annan.

Opposition activists say forces loyal to Bashar al-Assad attacked Homs on Saturday (April 14), and six people were killed in various incidents.

Video posted on a social media website showed thick smoke amid destroyed buildings, while several gun shots were heard.

Reuters is unable to independently to verify the content of these footages.

US Ambassador to the UN Susan Rice said the shelling of Homs was a violation of the ceasefire.

(SOUNDBITE) (English) UNITED STATES AMBASSADOR TO THE UNITED NATIONS, SUSAN RICE, SAYING:

"Even as the United States welcomes today's action by the Security Council, we're under no illusions. Just this morning Syrian forces resumed their brutal shelling of Homs and opened fire on mourners in Aleppo, raising renewed doubts about the sincerity of the regime's commitment to a ceasefire."

In this video, dozens of people in Allepo are shown running amid the sound of gun shots, while two men dragged an injured man.

The United Nations estimates that Assad's forces have killed more than 9,000 people in its crackdown on protesters. Syrian authorities continue to blame militants, and say more than 2,500 of their forces have been killed.

Michaela Cabrera, Reuters.