Drive-by attackers lobbed two grenades at the Saudi consulate in Pakistan’s largest city of Karachi on Wednesday, in a first possible violent reaction to the US killing of Osama bin Laden.

Officials reported no damage and no casualties after two men on a motorcycle threw the explosives at the heavily fortified building in Clifton, the smartest neighbourhood of Karachi, nine days after bin Laden was killed in Pakistan.

“This was an attack on the Saudi consulate. Two motorcycle riders threw two grenades and fled,” provincial government official Sharfuddin Memon told AFP.

“One exploded and hit the outer wall. The second landed inside and fortunately didn’t explode. It was later defused by bomb disposal,” he said.

“There were no casualties. We are seeing this incident in the present context. It could be a reaction of the Osama incident.” Pakistan has been in the grip of domestic and international crisis since US Navy SEALS flew in, seemingly undetected, from Afghanistan to identify and kill the Saudi-born Al-Qaeda terror mastermind at a suburban compound on May 2.

Pakistanis have expressed horror at the perceived impunity of the raid, furiously asking if their military was too incompetent to know he was living in a garrison city near the capital, or, even worse, conspired to protect him.

But while the killing has not ignited mass protests in the Muslim country, where more than 4,240 people have died in bomb attacks blamed on the Taliban and Al-Qaeda in the last four years, small gatherings have vowed revenge.

“We fear that desperate elements are planning to launch a big attack. We are taking precautionary measures in this regard,” Memon said.

Saudi Arabia expelled bin Laden in 1991 and later revoked his nationality. The government in Riyadh, which is allied to the authorities in Islamabad, last week welcomed his killing as a boost to international anti-terror efforts.

An AFP photographer said ambulances, police and paramilitary Rangers swarmed outside the Saudi consulate after the attack, where small shrapnel marks could be seen on the outer wall of the building.

Mohammed Safdar, a police official at the scene, said security guards at the diplomatic mission had opened fire on the attackers but they escaped.

“Two security men at the gate opened fire on them, but they managed to flee,” he told AFP.

“The security guards informed us and we reached the spot immediately. The bomb disposal squad are here. Other police and Rangers have surrounded the area,” he added.

Pakistan is holding in protective custody three of bin Laden’s widows, who come from Saudi Arabia and Yemen, and 13 of their children.

The foreign ministry says it has yet to receive a formal request from the United States for access to the relatives or requests from their home countries for their repatriation.