Two suicide bombers targeting the Pakistani military killed at least 45 people in Lahore Friday, officials said, in a challenge to government assertions that crackdowns have weakened Taliban insurgents.

A third bomb exploded near a police station in Lahore later Friday, police said, wounding up to four people and further rattling nerves in the eastern city near the border with India.

Militants have renewed pressure on the U.S.-backed Pakistani government, with five bomb attacks this week alone.

"Two suicide bombers attacked within the span of 15 to 20 seconds and they were on foot," provincial police chief Tariq Saleem Dogar told reporters after the earlier attack.

Those killed in that attack, the bloodiest this year, in a military neighbourhood included nine soldiers, military officials said. Almost 100 people were wounded.

Pakistani authorities have said security crackdowns have weakened al Qaeda-linked Taliban militants fighting to topple the government, which is under pressure at home and abroad.

But the Taliban have renewed pressure on unpopular President Asif Ali Zardari. A lull in violence could have provided some relief for Zardari, who faces calls from opponents to hand over his strongest powers to the prime minister.

If that does not happen, Pakistan could face new political turmoil while being pressed to defeat the Taliban.

The five blasts this week included a car bomb suicide attack on a police intelligence building in Lahore Monday that killed 13 people. A shooting and bombing at a U.S.-based aid agency killed another 6 in the northwest.

STUBBORN INSURGENCY

Kamran Bokhari, South Asia direc

tor at the STRATFOR global intelligence firm, said the blasts were not as sophisticated as others. He expected a new Taliban push.

"This new wave was expected as they are under pressure to demonstrate that, despite the several hits they have taken, they continue to sustain operational capability," he said.

Apart from facing a stubborn insurgency at home, Pakistan is also under heavy American pressure to open a new front and go after Afghan Taliban militants in border sanctuaries, a move that would tax its stretched military.

While Taliban bases have been smashed in government offensives in militant strongholds such as South Waziristan, fighters have a history of melting away to rugged areas which are hard for the military to penetrate.

"The militant network is not substantially or reasonably damaged and they are still capable of striking," said analyst Khadim Hussain.

A Reuters photographer said soldiers cordoned off the site of Friday's first two blasts and were not allowing anyone near. Troops were deployed on rooftops and an army helicopter flew overhead.

Rescue workers with stretchers rushed towards the blast site.

Police official Mohammad Shafiq told reporters the heads of both attackers had been found. Suicide bombers often strap explosives to their bodies and the blasts take off their heads.

Pakistani markets have mostly shrugged off violence, which has spread from militant strongholds in the northwest near the Afghan border to major cities.

The market temporarily dipped after the Lahore attacks, before Pakistani stocks ended on a more than 18-month high on foreign buying Friday, passing through the 10,000-point level. The Karachi Stock Exchange's benchmark 100-share index rose 146.29 points, or 1.48 percent, to end at 10,025.99.

(Additional reporting by Augustine Anthony, Zeeshan Haider and Sahar Ahmed; Writing by Michael Georgy; Editing by Paul Tait)