Suspected militants have killed at least five people in a bomb attack on a navy bus in the port city of Karachi.
Four of those who died in the roadside bombing were navy personnel. The fifth was a passing motorcyclist, officials said. Five others were wounded.
It is the third such attack this week. Four people died when two navy buses were bombed on Tuesday.
Officials believe the same group is behind the attacks. The Taliban say they carried out the bombings.
Correspondents say security officials in Karachi, the main base for Pakistan's navy, are also not ruling out a possible link to local Islamist groups.
Militant groups linked to the Taliban and al-Qaeda have carried out attacks in the southern city in the past.
The spate of bombings in Karachi is being seen as retaliation for an offensive against the Pakistani Taliban and their allies in the north-west of the country.
Thursday's bomb went off in the early hours of the morning in the Karsaz area of the city, along the busy Faisal Avenue. It tore through the bus and left a huge crater in the road.
"I was trying to cross the road a few feet away from the bus when I heard an explosion and saw the bus was hit and people inside and around crying," passer-by Asghar Ali told AFP news agency.
Police officials at the scene said they suspect the bomb was planted in a motorbike found near the blast site.
They said the attack appeared similar to Tuesday's twin bombings. The Taliban claimed the latest blast, as they did Tuesday's attacks.
"We are attacking the Pakistan army as it is supporting America against us," Taliban spokesman Ahsanullah Ahsan told The Associated Press by telephone from an undisclosed location.
This week's attacks on naval personnel follow a blast a week ago at a gambling club, in which at least 18 people were killed.
Police said they suspected Islamist militants carried out that attack.
Pakistan's commercial capital has also been hit by a wave of political and ethnic attacks blamed on local gangs. Hundreds have been killed over the past year.