Twelve people were killed and a number of others held hostage in a highly co-ordinated attack by Pakistani militants that resulted in two high-value U.S.-made planes being destroyed.

Pakistani commandos managed to put an end to the siege on Monday and regain control of the naval base in Karachi after an 18-hour standoff.

CTV's South Asia Bureau Chief Janis Mackey Frayer said the Pakistani Taliban claimed responsibility for the bold attack, which was reportedly carried out to avenge the death of Osama bin Laden by U.S. forces on May. 2.

"There have been other attacks primarily on Pakistani military targets," Mackey Frayer said, reporting from New Delhi.

"But this one was so bold, so co-ordinated, so sophisticated that it's raising familiar questions, not only about the vulnerability of Pakistan's security forces but their ability to protect its nuclear arsenal."

There are believed to have been six militants involved in the attack. At least four of the militants were killed in the fighting.

According to a statement from the Pakistani Taliban on Monday, the attackers were under orders to fight until the death.

"They do not want to come out alive, they have gone there to embrace martyrdom," said spokesman Ahsanullah Ahsan.

Mackey Frayer said the insurgents, who were armed with grenades, rockets and automatic weapons, stormed Naval Station Mehran late Sunday using ladders to break into the facility.

"The militants stormed the naval base and headed for three hangars where they set ablaze two premier U.S.-made attack jets and then started firing indiscriminately," Mackey Frayer said.

Once inside the hangars, the militants began setting off explosives and firing at troops.

For most of Monday, they hid out in an office building while engaging in a gunfight with commandos, navy spokesperson Irfan ul Haq told The Associated Press.

Navy helicopters and snipers were all involved in the battle.

On Monday afternoon Haq reported that "Thanks be to God, the base is cleared and the operation is over."

He said 11 navy personnel were killed, along with one paramilitary ranger. Another 14 security forces were wounded.

While four of the militants were killed, another two may have escaped, Haq said.

According to some eyewitness reports the militants were dressed in black.

Monday's violence represents the third major attack since bin Laden was killed on May 2 in a covert raid by U.S. forces on the compound where bin Laden was living in the garrison city of Abbottabad in northwest Pakistan.

Militants also carried out a car bombing that injured an American consul worker in Peshawar and a double-suicide bombing that killed about 90 paramilitary recruits outside a training school.

Pakistan's security leaders have faced tough criticism over the fact bin Laden's presence apparently went undetected for years.

Mackey Frayer said Monday's attack is raising more questions about Pakistan's security capabilities.

The apparent ease with which the militants penetrated the base raised the possibility they may have had inside help.

Pakistani Prime Minister Yousuf Raza Gilani said the attack was a "cowardly act of terror could not deter the commitment of the government and people of Pakistan to fight terrorism."

The military planes that were targeted at the naval base were P-3C Orions -- surveillance aircraft given to Pakistan by the U.S.

At least two were destroyed, a total loss valued at about US$72 million.

With files from The Associated Press