Gunmen on a motorbike shot and killed a Saudi diplomat as he was driving in Pakistan's largest city on Monday, just days after two hand grenades were tossed at the Arab state's consulate building, police in Karachi said.

The police believe the primary motive was sectarian tension between Islam's Sunni and Shiite branches. But the attack also follows the killing of Saudi-born Osama bin Laden in an American raid on May 2.

Al-Qaida is a fierce opponent of the Saudi regime and has sworn revenge for the death of bin Laden. But no one immediately claimed responsibility for the diplomat's slaying.

A spokesman for the Pakistani Taliban, the country's most high profile militant group, called The Associated Press to say it did not kill the diplomat.

The spokesman, Ahsanullah Ahsan, added: "Although we believe Saudi Arabia is an even bigger slave to America than Pakistan, we are not involved in today's killing."

Tariq Dharejo, a police investigator in Karachi, said officers believe the shooting was motivated by anger over Saudi Arabia's decision to send troops to Bahrain to quell protests by Shiites, who comprise 70 percent of the population there but are excluded from key positions in the Sunni-dominated government. Saudi Arabia is almost entirely Sunni.

Sunni-Shiite tensions trace back to a seventh century dispute over the true heir to Islam's Prophet Muhammad.

Monday's attack took place not far from the consulate building. The diplomat — who was driving a silver Toyota Corona and was alone — appeared to be on his way to work, said police officer Zameer Husain Abbasi. He said a 9 mm pistol was used in the assault.

The victim, identified as Hasan Khattani, was a member of the security staff at the consulate, said Iqbal Mehmood, Karachi's deputy inspector of police. He said the shooting was carried out by two men on a motorbike and appeared to be linked to last week's grenade attack on the mission, which caused some damage but no injuries.

The Saudi Foreign Ministry condemned the diplomat's killing and said in a statement issued Monday that Saudi Arabia has asked Pakistani authorities to increase security measures around the Saudi embassy and consulate in Pakistan. Prince Saudi al-Faisal, the statement said, gave condolences to the family of the slain diplomat.

Officials at the Saudi mission were not immediately available for comment.

In a statement, Pakistani Prime Minister Yousuf Raza Gilani condemned the attack and "expressed deep grief and sorrow over the tragic death of the Saudi diplomat."

Pakistan's alliance with Sunni rulers in the Middle East has come under the spotlight since the uprisings there this year. A company with strong links to the country's army announced it was sending 1,000 Pakistanis to Bahrain to help its security forces put down the Shiite uprising.

Karachi is a violent southern city of 18 million people that has been a cauldron of ethnic, sectarian and political tensions.

Saudi Arabia has funded hardline Sunnis, Iran has channeled money to Shiite groups, and in the 1980s and 1990s the country was the scene of an effective proxy war between Iran and Saudi Arabia, with Karachi an especially bloody battleground.

Several of Pakistan's Sunni extremist groups also are allied with al-Qaida and the Taliban, who view Shiites as infidels.

Saudi Arabia stripped bin Laden of citizenship and has fought al-Qaida. But money from some of its citizens is believed to help bankroll the terrorist network, which has carried out scores of attacks inside Pakistan over the last 10 years.


Khan reported from Islamabad.