A bomb blast at a mosque in Pakistan's northwestern tribal belt killed 29 people including some militants Thursday, underscoring the relentless security threat here even as Pakistani-US cooperation against extremism appears on the upswing. The attack in Khyber tribal region came as US special envoy Richard Holbrooke met with Pakistan's prime minister in Islamabad, the capital. It also followed revelations that Pakistani authorities have been picking up Afghan Taliban leaders on their soil, a longtime US demand. The explosion tore through a mosque in the Aka Khel area of Khyber, killing at least 29 people and wounding some 50 others, local official Jawed Khan said. Earlier reports had said the blast occurred in the Orakzai area at a cattle market. Officials were still investigating whether the explosion was caused by a suicide bomber or a planted device. No group claimed responsibility, but Khan said the dead included militants from Lashkar-e-Islam, an insurgent group in Khyber that has clashed with another militant outfit known as Ansarul Islam. Both espouse Taliban-style ideologies. Pakistani Prime Minister Yousaf Raza Gilani told Holbrooke that the US should take into account Pakistan's concerns that the Marjah offensive could lead to Afghan refugees and militants heading to Pakistan's southwest and northwest, according to Gilani's office. The pair also discussed US humanitarian aid efforts, with Gilani pressing for a quicker release of funds. The US has pledged $7.5 billion in aid to Pakistan over the next five years. Talking with reporters in Kabul on Wednesday, Holbrooke said the US was restructuring the way it doles out aid to Pakistan and intends to consult more with the Pakistanis and pursue more visible projects. “It is very, very time consuming work because of the huge, long lead times of contracts, because of the congressional role,” he said.