Video posted to a social media website purports to show heavy shelling in Homs - a city that has become the bloody epicentre of a year-long revolt against Syrian President Bashar al-Assad's government.<br/> <br />The video upload date is shown as the 7th of April, but a male voice is heard describing the shelling as taking place on April 8.<br/> <br />Reuters is unable to independently verify the content of this footage.<br/> <br />Opposition activists say 74 civilians have been killed in a country-wide offensive by Syrian troops ahead of next week's U.N.-backed ceasefire.<br/> <br />At least 15 rebels and 17 security force members were also killed.<br/> <br />Each side has accused the other of intensifying assaults before the truce.<br/> <br />International mediator Kofi Annan says there's been an "unacceptable" escalation in violence.<br/> <br />He's called on the Syrian government to keep to pledges to end the bloodshed before Tuesday's deadline.<br/> <br />Syria says it wants "written guarantees" from insurgents that they will stop fighting, before it pulls troops back.<br/> <br />According to the U.N., more than 9,000 people have been killed since security forces unleashed a crackdown on rebels and civilians just over a year ago.<br/> <br />Travis Brecher, Reuters
