At least 18 people have died in Lebanon after a bomb exploded on a bus in Tripoli.

A further 40 people were wounded, two of them seriously, in a busy area of Lebanon's second largest city.

At least seven of the dead are soldiers. One estimate puts the number of dead troops at 11.

TV footage showed a small public bus riddled with shrapnel from the blast. hattered glass could be seen in the street, in Tripoli’s center.

Nobody has claimed responsibility for the attack.

Tripoli lies to the north of Lebanon and has a mostly Sunni Muslim population. In the past weeks the city has witnessed sectarian clashes between Sunni fighters and followers of the Alawite sect - an offshoot of Shia Islam, and the religious grouping of Syrian ruler Bashar al-Assad - which have killed and wounded dozens of people.

The city is also close to the Palestinian refugee camp of Nahr el-Bared, which experienced deadly clashes last year between Lebanese troops and members of the al-Qaeda-inspired Fatah al-Islam group. Hundreds of people died in the protracted siege, including 170 soldiers, before the militants were defeated.

Fatah al-Islam claimed responsibility for a bomb blast that killed a soldier in Abdeh near Tripoli on May 31.

The latest violence comes at an especially sensitive time for Lebanon.

Yesterday, after a five-day debate and weeks of negotiations, the country's parliament approved a national unity government that gives the Iranian and Syrian-backed Hezbollah opposition a more powerful say in the running of the country, including veto power over major decisions.

The explosion also comes as Michel Suleiman, the Lebanese President, is due to make a landmark visit to Syria, Lebanon's much larger neighbour which has been accused of repeated interference in Lebanon's internal affairs.