(Adds Taliban claim)
By Faisal Aziz and Imtiaz Shah
KARACHI, April 26 (Reuters) - Taliban militants attacked two buses carrying navy officials in Pakistan's southern city of Karachi on Tuesday, killing four people and wounding 56, officials said, the first major attack on the military in the city in seven years.
Police said the bombs targeting the buses in two different parts of the city exploded simultaneously using remote controlled devices.
A junior naval officer and a civilian female doctor were among those killed in the twin blasts, Pakistan Navy spokesman Commander Salman Ali said.
The Taliban claimed responsibility for the attacks, and vowed more attacks on security forces.
"Security forces will be targeted in the future as well, because they are killing their own people in Waziristan and elsewhere on the behest of the United States," Taliban spokesman Ehsanullah Ehsan told Reuters by telephone from an undisclosed location.
Analysts said that the attacks may be part of a wider militant campaign to hit security forces across the country.
"It appears to be part of the same militant campaign but I don't see any logic in targeting the navy because unlike army and air force they are not involved in any operations against the militants," said Tasneem Noorani, a security analyst and former interior secretary.
"They may have targeted navy out of desperation because the other forces may have become very careful and are difficult to attack."
The attack on the military in Karachi was the first since 2004, when gunmen ambushed a convoy escorting the Karachi army corps commander. The general narrowly escaped that attack.
Karachi is Pakistan's biggest city and commercial hub. It hosts the country's central bank, the main stock exchange as well as the two main ports. Most foreign companies working in Pakistan have offices in Karachi, which is also the main base for the navy.
"Explosive devices were planted on the road and they exploded as the buses were passing. Both buses were carrying navy officials," senior police officer Iqbal Mahmood said.
In 2002, 11 French engineers and technicians working on the construction of submarines for the Pakistani navy were killed, along with three Pakistanis in a suicide car bombing outside a hotel in Karachi.
Separately, gunmen attacked and set fire to a bus in Pakistan's southwestern Baluchistan province late on Monday, burning 15 people to death, including four children and two women, a senior government official said.
The attack took place in Sibi town, about 160 km (100 miles) east of the provincial capital of Quetta when the bus was parked at a roadside restaurant.
Ethnic Baluch militants have waged a low-level insurgency for decades for more autonomy and greater control of natural resources of their region. They frequently attack government installations and security forces in their violent campaign. (Additional reporting by Zeeshan Haider in Karachi, Gul Yousafzai in Quetta, Saud Mehsud in D. I. Khan and Mian Khursheed in Islamabad; Editing by Alex Richardson)
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