Pakistani soldiers cordon off the area of a suicide bombing in Lahore, Pakistan, on Friday. (K.M. Chaudary/AssociatedPress)

Suicide bombers targeting army vehicles detonated explosives within seconds of each other in the eastern Pakistani city of Lahore, killing at least 43 people. Nearly 100 people were wounded.

The twin blasts were the fourth major attack in Pakistan this week, indicating Islamist militants may be stepping up assaults in Pakistan after a period of relative calm.

The bombers struck RA Bazaar, a residential and commercial neighbourhood where several security agencies have facilities. Pakistani TV channels showed security forces swarming the area as bystanders rushed the injured into ambulances.

About 10 of those killed were soldiers, said Chief Parvaiz Rathore of the Lahore police.

Eyewitness Afzal Awan said he saw several people, some missing limbs, lying in pools of blood after an enormous explosion.

"I saw smoke rising everywhere," Awan told reporters. "A lot of people were crying."

Taliban, al-Qaeda suspected

Video shot with a mobile phone just after the first explosion showed a large burst of orange flames suddenly erupting in the street, according to GEO TV, which broadcast a short clip of the footage shot by Tabraiz Bukhari.

"Oh my God! Oh my God! Who are these beasts? Oh my God!" Bukhari can be heard shouting after the blast in a mixture of English and Urdu

No group immediately claimed responsibility, but suspicion quickly fell on the Pakistani Taliban and al-Qaeda.

Hours later, a series of five smaller blasts injured three people and spread fear in another section of Lahore. There were no reports of death or major damage.

The militants are believed to have been behind numerous attacks in Pakistan over the last several years, including a series of strikes that began in October and lasted around three months, killing some 600 people in apparent retaliation for an army offensive along the Afghan border.

More recent attacks had been smaller and confined to remote regions near Afghanistan, but on Monday, a suicide car bomber struck a building in Lahore where police interrogated high-value suspects.

At least 13 people died and dozens were wounded in the attack, for which the Pakistani Taliban claimed responsibility.

The violence comes amid reports of a crackdown on Afghan Taliban and al-Qaeda operatives using Pakistani soil. Among the militants known to have been arrested is the Afghan Taliban's No. 2 commander, Mullah Abdul Ghani Baradar.

Also this week, suspected militants attacked the offices of World Vision, a U.S.-based Christian aid group, in the northwest district of Mansehra, killing six Pakistani employees, while a bombing at a small, makeshift movie theatre in the northwest city of Peshawar killed four people.

A Pakistani woman mourns a family member killed in one of the suicide bombings in Lahore on Friday. (K.M. Chaudary/Associated Press)

Rana Sanaullah Khan, the law minister for Punjab state, where Lahore is located, said the renewed attacks are a "sign of desperation" by the militants.

"We broke their networks," he said. "That's why they have not been able to strike for a considerable time."

The Pakistani Taliban, meanwhile, are believed to have lost their top commander, Hakimullah Mehsud, in a U.S. missile strike in January. The group has denied Mehsud is dead but has failed to prove he's still alive.

Militant attacks in Pakistan frequently target security forces, though civilian targets have not escaped. During the bloody wave of attacks that began in October — coinciding with the army's ground offensive against the Pakistani Taliban in the South Waziristan tribal area —Lahore was hit several times.

In mid-October, three groups of gunmen attacked three security facilities in the eastern city, a rampage that left 28 dead. Twin suicide bombings at a market there in December killed about 50 people.