Syrian forces stormed the last rebel stronghold in the capital Damascus in tanks and armoured vehicles on Friday, August 3 and blasted artillery at rebels in Aleppo, where the United Nations said the army was preparing a massive assault, according to Reuters.

The violence came within hours of former United Nations Secretary-General Kofi Annan quitting as international peace envoy for Syria, underlining the impotence of mediation efforts in the 17-month-old uprising against President Bashar al-Assad.

A senior U.N. official said a long-expected army onslaught to take Aleppo, Syria's largest city and economic hub, was imminent following a buildup of army reinforcements. The fighting in Aleppo has focused on the Salaheddine district, seen as a gateway to the city for the Syrian army.

Rebels poured into Aleppo in July after being largely driven from the capital, Damascus, where they had launched an offensive that coincided with a bomb blast that killed four top security officials. The fighting in Syria's two main cities has intensified the conflict over the past three weeks.

Rebels told Reuters journalists inside Aleppo on Friday that they had captured a large police station after days of clashes. Rebel commander Abu Zaher said fighters had taken several police officers prisoner and seized weapons and ammunition.