Pakistani security forces have arrested an Uzbek al-Qaeda militant suspected of helping to plan a suicide car bombing that killed a US diplomat and three others outside the US consulate in Karachi in March, officials said on Wednesday.
The suspect was arrested two weeks ago in Wana, the main town in South Waziristan, a tribal region bordering Afghanistan, according to an official in the provincial Sindh government, who requested anonymity.
The Pakistan army launched an offensive over two years ago in South Waziristan to drive out nests of Arab, Chechen and Central Asian al-Qaeda fighters.
"The arrested Uzbek told the investigators that the plan was made by an al Qaeda group in Waziristan," the official said.
"They however, used a local militant group to execute their plan."
Two other officials close to the investigation in Karachi gave the same account, though an official at the Interior Ministry in Islamabad denied any such arrest had been made.
"The information is totally negative and there is no truth in it," Javed Iqbal Cheema, head of the ministry's crisis management cell, said.
The attack which killed diplomat David Foy took place on March 2, the eve of a visit by US President George W Bush to Pakistan.
Police at the time said they suspected Islamist militants opposed to President Pervez Musharraf's support for the US-led war on terrorism.
The attack was well-planned, with the driver of a white Toyota Corolla packed with explosives ramming Foy's car just metres (yards) away from the U.S. Consulate's main gate.
The blast also wounded 52 people.
An official close to the investigation said security agencies were hunting another Uzbek hiding in the border region, who is believed to have been the main planner of the attack.
"The Uzbek, who is on the run, is the ringleader of the group, and that person had planned the attack," the official said, without giving any further details.
Many al-Qaeda members fled to the rugged Waziristan region after US-backed forces ousted the Taliban and al-Qaeda from Afghanistan in late 2001.
In May, Pakistani police arrested two local militants suspected of being involved in the attack. They belonged to Lashkar-e-Jhangvi, a Sunni Muslim militant group that has forged links with al-Qaeda, though it is also behind many attacks on Pakistan's minority Shi'ite Muslim community.