Smoke clung to the skyline in Homs and just as it appeared to be clearing, another explosion --- as activists reported government forces were intensifying their assault on the city.
Reuters cannot independently verify the content of this video, which was posted to a social media website.
The heaviest shelling was directed at a part of Homs inhabited mostly by Sunni tribal families and there are reports that rebel outposts in Rastan and other parts of central Syria are also under heavy fire.
UN efforts to bring peace to Syria - where a 15-month-old uprising against Assad has turned increasingly violent - have largely come to nothing.
In Geneva, a spokesperson for mediator Kofi Annan expressed concerns that locals could be trapped in targeted areas.
Ahmad Fawzi.
SOUNDBITE: Kofi Annan's Spokesperson, Ahmad Fawzi saying:
"Mr. Annan is particularly worried about the recent shelling in Homs as well as reports of the use of mortar, helicopters and tanks in the town of al-Haffeh in Latakia."
Activists say at least 35 people were killed on Monday.
Deborah Gembara, Reuters.
