Suspected Al-Qaeda gunmen killed five guards and captured others Friday in an attack on a checkpoint outside the Yemeni presidential palace in the capital Sanaa, a security source said.

Suspected Al-Qaeda gunmen killed five guards and captured others Friday in an attack on a checkpoint outside the Yemeni presidential palace in the capital Sanaa, a security source said.

The source told AFP that President Abdrabuh Mansur Hadi was not at the palace at the time of the attack, which came amid heightened tensions in Yemen where the army is pressing an offensive against Al-Qaeda militants.

The gunmen "attacked a checkpoint manned by presidential guards in Sanaa, killing five soldiers and capturing a number of others," the source said, adding there were unconfirmed reports that the dead included two of the assailants.

Security sources and witnesses said there was an exchange of fire and that the gun battle lasted more than 20 minutes.

Sanaa has been on alert for days, and tensions rose when the army announced troops had entered Azzan, a major militant bastion in the southern province of Shabwa, prompting the closure on Thursday of the US embassy.

Late Thursday security forces killed Al-Qaeda commander Shayef Mohammed Said al-Shabwani, who was suspected of masterminding the abduction of Western diplomats and of involvement in killing policemen.

He was killed in a shootout near the presidential palace.

The building, also known as the republican palace, is the official headquarters of the president where he has his office and receives guests.

But the president does not live there and was not present at the time of Friday's attack, the security source said.

Earlier on Friday, 11 policemen were wounded when a bomb exploded in a bus in an eastern district of the city where the British and Qatari embassies are located.

And later in the day the defense minister and two senior security officers were ambushed as their convoy returned from a tour of the battleground in the south where the army is fighting militants.

Authorities say Al-Qaeda commanders were among dozens of militants killed since the army launched its offensive 11 days ago in the south, where US drone strikes this year have killed scores.

The interior ministry has warned the militants will resort to "hysterical and desperate acts" because of the "huge losses" they have suffered since April 29.