Gunmen opened fire on a car belonging to the Saudi consulate in Karachi, killing a Saudi citizen, police said.
Hassan al-Qahtani, a consulate employee, was attacked in the wealthy and normally peaceful Defence district.
The attack comes two days after grenades were thrown at the consulate building, causing no injuries.
No group has said it carried out the attack, but al-Qaeda is known to be violently opposed to the Saudi government.
The group has vowed to avenge the death of its Saudi-born leader Osama Bin Laden, who was killed in a US raid in Pakistan earlier this month. Saudi Arabia stripped the al-Qaeda leader of citizenship years ago.
A Taliban spokesman told the BBC that while they did not carry out this attack, they supported whoever did.
A Saudi official told the AFP news agency that the attack took place about 1km (half a mile) from the consular building.
"At least six bullets were fired in the attack," Deputy Inspector General of Police Iqbal Mahmood told reporters.
"There were four men on two motorbikes and they stopped the vehicle before opening fire," he said.
Saudi ambassador Abdul Aziz al-Ghadeer condemned the attack. "No-one who carries out this kind of attack can be a Muslim," he told the Reuters news agency.
The southern port city of Karachi has seen an increase in violence in recent years. There have been Taliban attacks on the city and ethnically-based political and sectarian killings are common too.