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 he would be transferred to Pakistan after undergoing medical checks.

Ali Haider Gilani was kidnapped three years ago in Multan as he was campaigning in elections for the Pakistan Peoples' Party (PPP).

The Taliban were long believed to be behind the kidnapping.

PPP chairman Bilawal Bhutto tweeted the news, saying the captive had "been recovered in a successful operation".

Pakistan's foreign ministry confirmed it had received the news from Afghan security officials.

Bargaining chips

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 2013 elections. He was seized by gunmen who opened fire on a campaign rally in May 2013, two days before the general election.

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 was also a tactic frequently used by militant groups across Pakistan, who needed the ransom money for revenue and used the hostages as bargaining chips in negotiations with the authorities.