Media playback is unsupported on your device Media caption Ali Haider Gilani's brother said they were unaware of the operation to free him

The kidnapped son of Pakistan's ex-Prime Minister Yusuf Raza Gilani has been rescued in Afghanistan in a joint Afghan-US special forces operation.

Pakistani officials said Ali Haider Gilani would be transferred to Pakistan after undergoing medical checks.

Mr Gilani was abducted three years ago in his home town of Multan as he was campaigning in elections for the Pakistan Peoples' Party (PPP).

The Afghan envoy to Pakistan said he was held by an al-Qaeda-linked group.

"He is well and will be repatriated to his family soon," Dr Omar Zakhilwal said on his Facebook page.

Celebrations

The Nato-led mission in Afghanistan said he had been rescued in a joint operation in the eastern Paktika province, not in neighbouring Ghazni as earlier reported.

"The counter-terrorism mission was planned and launched after evidence of terrorist activity was confirmed," the Resolute Support mission said in a statement.

"Four enemy combatants were killed as a result of the operation. No other injuries or damage was observed or reported."

Ali Haider Gilani's brother, Ali Musa Gilani, told the BBC he had been caught unaware by the release, with the family not told about the operation.

"He [Ali Haider Gilani] called himself from an Afghanistan number, and he just told me, 'I have US military around me, and they have rescued me, and now what are you doing? Who are you getting in touch with to get me out of here?'"

Television pictures showed celebrations in Multan. At a party rally in Pakistan-administrated Kashmir, his father was seen surrounded by well-wishers.

The newly released captive has been taken to Bagram airbase in Afghanistan and will be transferred to Pakistan in a few hours, Geo TV reports.

Media playback is unsupported on your device Media caption Mike Wooldridge was in Islamabad in 2013 and reported on the kidnapping

Ali Haider Gilani is the youngest son of Yusuf Raza Gilani, who was prime minister of Pakistan from 2008 until 2012.

He had been contesting a seat in the Punjab provincial assembly in the May 2013 elections, when he was seized by gunmen who opened fire on a campaign rally just a few days before the polls opened.

Suspicion immediately fell on the Pakistani Taliban, which had been openly threatening the governing PPP and other secular parties in Pakistan in the run-up to the election.

Kidnapping has frequently been used as a tactic by militant groups across Pakistan, who want the ransom money for revenue and use the hostages as bargaining chips in negotiations with the authorities.

Yusuf Raza Gilani said last year that he had been allowed to speak to his son for several minutes by phone, and that the kidnappers wanted the release of several high-profile al-Qaeda prisoners.

In March, the kidnapped son of Pakistan governor Salman Taseer was found alive, nearly five years after his father was assassinated and he was seized in Lahore.

Shahbaz Tasser was recovered by counter-terrorism police in a compound north of Quetta, just a few days after his father's killer - his bodyguard Mumtaz Qadri - was hanged.