Syria's prime minister survived a bomb attack on his convoy in Damascus, as rebels struck in the heart of President Bashar al-Assad's capital.

Six people were killed in the blast, the British-based Syrian Observatory for Human Rights said.

Previous rebel attacks on government targets included a December bombing which wounded Assad's interior minister.

As prime minister, Wael al-Halki wields little power but the attack highlighted the rebels' growing ability to target symbols of Mr Assad's authority in the civil war.

President Assad picked Mr Halki in August to replace Riyadh Hijab, who defected and escaped to neighbouring Jordan just weeks after a bombing killed four of the president's top security advisers.

The blast shook the Mezze district shortly after 9am (7am Irish time), sending thick black smoke into the sky.

The Observatory said one man accompanying Halki was killed as well as five passers-by.

State television showed firemen hosing down the charred and mangled remains of a car. Close by was a large white bus, its windows blown out and its seats gutted by fire.

Glass and debris were scattered across several lanes of a main road.

In comments released by the state news agency SANA but not shown on television, Mr Halki was quoted as condemning the attack as a sign of "bankruptcy and failure of the terrorist groups".

Mezze is part of a shrinking "Square of Security" in central Damascus, where many government and military institutions are based and where senior officials live.