Pakistani officials say a roadside bomb has hit a bus carrying navy personnel in Karachi, killing five people, in the third such attack this week.
Thursday's blast killed four navy employees and a civilian on a motorcycle. Five people were wounded and nearby buildings and vehicles were damaged in the bombing.
The Taliban has claimed responsibility for the attack, as well as for a pair of blasts Tuesday that also targeted buses carrying navy personnel in the southern port city. Those attacks killed four people and wounded more than 50 others.
A Taliban spokesman on Thursday vowed more strikes against security forces.
Pakistani Prime Minister Yousuf Raza Gilani condemned the attack and called for an investigation.
Karachi is Pakistan's economic hub and its largest city with roughly 16 million people. It has been plagued by criminal, sectarian and militant violence. The Pakistani navy is based in the city, which is located on the coast of the Arabian Sea.
Security experts say the navy was a soft target and that attacks in Karachi could be a sign that militants are expanding their reach beyond the country's northwest.
The attacks come days after Pakistan's army chief said his forces have "broken the back" of insurgents linked to the Taliban and al-Qaida. Army General Ashfaq Kayani said Saturday that Pakistan is fully aware of the internal and external threats to the country.
Pakistan has launched several offensives against militants in the northwest along the Afghan border, but bombings and suicide attacks have continued.
Earlier this month, the United States criticized Pakistan's counterterror efforts, saying the country had no clear path to defeating Taliban and al-Qaida-linked militants in the border region.
The top U.S. military commander, Admiral Mike Mullen, also said some members of Pakistan's military intelligence agency have a long-standing relationship with Haqqani militants fighting in Afghanistan.
Pakistan has denied any link with the al-Qaida affiliated group, and Kayani has rejected criticism of the country's efforts in the war on terrorism.
Some information for this report was provided by AP, AFP and Reuters.