Pakistan (Reuters) - A suicide bomber on a motorbike killed up to 45 people and wounded dozens in an attack outside the office of a senior government official in Pakistan's northwest on Friday, government and hospital officials said. The bomber struck when people were gathered around the office in the Mohmand ethnic Pashtun tribal region on the Afghan border, where security forces have stepped up attacks on Taliban militants in recent weeks.

"There were two blasts. The first one was small but the second was a big one. Up to 45 people have been killed," Rasool Khan, the region's assistant political agent, told Reuters. The attack took place outside his office.

An administration official, Mehraj Khan, had earlier described the incident as a suicide attack, but there were no details available on how the second blast happened.

Hospital officials said nearly 80 people were being treated for multiple wounds, while government officials put the number of wounded at about 40.

Among the wounded were several internally displaced people, who were collecting relief goods near the blast site.

Thousands of people have been uprooted by the militant violence and security forces' operations in the northwestern region.

"I was standing about 200 yards (meters) away from the office when I heard the blast. I don't know how it happened but I could see several bodies lying on the ground after the explosion and people running in all directions," said Riaz Hussain, a witness.

Television footage showed victims being pulled out of the debris. The blast also damaged several cars and about 30 shops, witnesses said.

A security official at the scene said the blast also damaged a nearby prison wall and several inmates had escaped.

Pakistan launched two major offensives in the northwest last year against homegrown Taliban militants who have killed hundreds of people in retaliatory attacks across Pakistan, mostly in the northwest, but also in major cities.

Two suicide bombers killed at least 42 people in an attack on Pakistan's most important Sufi shrine in the eastern city of Lahore last week.

The Pakistani Taliban, allies of the Afghan Taliban, have lost ground in army offensives over the past year.

They were pushed out of the Swat valley, northwest of Islamabad, and in October the army began an offensive in the militants' South Waziristan bastion on the Afghan border.

The offensive was extended to Orakzai in March as many of the militants who fled the South Waziristan operation took refuge there and in Mohmand. Hundreds of militants have since been killed in air strikes in the two regions.

Jet fighters killed about a dozen militants in attacks in Orakzai on Friday, security officials said. There was no independent verification of the casualties as militants often dispute and reject official figures.

(Writing by Augustine Anthony; Editing by Chris Allbritton and Sugita Katyal)

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