Attack comes days after attackers threw two hand grenades at Saudi consulate in Pakistan
Gunmen on motorcycles shot and killed a Saudi diplomat in the Pakistani city of Karachi on Monday, police and the Saudi ambassador said, the second attack on the mission since the killing of Osama bin Laden increased tension in the region.
Pakistan's Taliban claimed responsibility, and warned the United States against attacking its close ally al Qaeda.
Al Qaeda has waged a bloody campaign to topple the royal family and government of Saudi Arabia, the birthplace of its leader bin Laden. The group has also vowed to avenge his killing by US special forces in a Pakistani military town on May 2.
Four people riding motorcycles opened fire on the Saudi diplomat's car, a Karachi police official said. The diplomat, a low ranking security official, was on his way to the consulate when the assailants struck.
Pakistan's interior minister condemned the attack and ordered Karachi authorities to provide "complete security" to Saudi nationals stationed in the city, where analyst say militants generate funds through extortion and robberies.
"We condemn this attack. No one who carries out this kind of attack can be a Muslim," the Saudi ambassador, Abdul Aziz Al Ghadeer, said. Four bullets were fired and one struck the diplomat in the head, said senior Karachi police official Iqbal Mehmood.
The Saudi state news agency named the diplomat as Hassan Al Qahtani and described his killing as a "criminal attack". It said Saudi officials would investigate the shooting alongside the Pakistani authorities.
The shooting, which a Saudi embassy official said occurred about 60 metres (200 feet) from the consulate, came days after unidentified attackers threw two hand grenades at the consulate in Pakistan's commercial hub. No one was hurt in that attack.
Saudi Arabia, one of the US' most strategic allies, is the world biggest oil exporter and any signs that its security is threatened could move global oil prices.
A Saudi Interior Ministry official, who declined to be identified, told Reuters in Dubai that security would be stepped up to protect Saudi diplomats living in "dangerous" areas.
Pakistan and Saudi Arabia have long been close allies and Islamabad needs all the support it can get after the discovery of bin Laden embarrassed the South Asian country.
"We trust the Pakistani authorities and hope they will identify the terrorists and bring them to justice," ambassador Al Ghadeer said.
Before claiming responsibility for the shooting, Pakistan's Taliban had described Pakistan and Saudi Arabia as American "slaves" and hailed the attack as a "very good job".
Saudi Arabia has its own internal security to worry about, not just the safety of diplomats who may be targeted.
Militants swearing allegiance to al Qaeda attacked Western targets, government sites and oil facilities in Saudi Arabia, between 2003 and 2006.
The operations included suicide bombings at Western housing compounds, the Saudi Interior Ministry headquarters in the capital Riyadh and petrochemicals companies.
Saudi Arabia responded with a largely successful security crackdown in 2007 and 2010, arresting more than 170 suspects, including some trainee pilots preparing for suicide attacks.
Analysts, however, suggested Saudi policy in Pakistan backfired.
Saudi Arabia, which is home to the fundamentalist Wahhabi brand of Islam, is seen as funding some of Pakistan's hardline religious seminaries which churn out young men eager for holy war, posing a long-term threat to the stability of the region.
"The Saudis have led a pretty successful campaign to root out al Qaeda and its extremists in Saudi Arabia over the last decade or so," said Salman Shaikh, director of Brookings Doha Centre, a policy research institute.
"I have to say that Saudi Arabia has had a mixed history in Pakistan as well. Many have accused it or certainly elements of its religious establishment of financing extremist education [in Pakistan] over the years."