One of Pakistan's most vicious militant groups has dramatically stepped up its attacks over the past month, striking mosques, Christians and security forces in attacks that have killed more than 60 people in what appears to be a backlash to military operations against it.

Ever since it broke away from the Pakistani Taliban in 2014, Jamaat-ul-Ahrar or the Freedom Movement had been carrying out sporadic attacks, often weeks or months apart. But since the beginning of September, it has struck 10 times, including a horrific bombing of a mosque earlier this month that killed 36 people, many of them children.

The spike in violence points to how Jamaat-ul-Ahrar, which the U.S. declared a terrorist organization last month, has eclipsed the Pakistani Taliban as the main, most aggressive militant group in a country where multiple armed extremist factions operate.

The Pakistani Taliban, or Tehrik-e-Taliban, have been struggling in the face of a two-year offensive by the military against its bases in North Waziristan, along the Afghan border. The assault has hampered its ability to carry out attacks and fueled splits by factions breaking away from the movement.

In contrast, Jamaat-ul-Ahrar has continued its blows even after military assaults on its home territory in Mohmand, another tribal area in the northwest of the country along the border with Afghanistan. It gained notoriety in late 2014 when it took responsibility for a vicious attack on a public army school that killed 125 people, most of them children, and again in early 2016 with a series of brutal attacks, including suicide bombings against Christians in Lahore on Easter that killed more than 70 people.

In a sign of its success, other groups have tried to claim responsibility for its attacks. For example, the Islamic State group — which has been trying to make inroads into Pakistan — made a competing claim to have carried out an August suicide bombing in the southwestern city of Quetta that killed nearly 80 people, mostly lawyers. But security officials say they believe Jamaat-ul-Ahrar was behind the attack.

A counter-terrorism official in northwestern Pakistan said Jamaat-ul-Ahrar is the most extreme of the militant groups operating in the Afghanistan-Pakistan border region and poses a "serious challenge" to security forces. He spoke on condition of anonymity because he is not authorized to speak to the media.

Pakistan's military in recent weeks picked up chatter among Jamaat-ul-Ahrar militants that warned of increased attacks, said Mahmood Shah, a retired army brigadier and former military intelligence official, who still has close military ties.

The chatter resulted in stepped up security which thwarted a Sept. 2 assault on a Christian colony in the northwestern city of Peshawar and an attempt last week to blow up a Shiite mosque in Punjab. Security officials stopped the attackers before they could reach their destinations.

Still, the group's fighters succeeded in carrying out a string of 10 other attacks. Among them was a bombing of a courthouse in the northwestern city of Mardan that killed 12 people. Most of its attacks were against security forces or other officials in Mohmand or nearby Peshawar city, but it also carried out bombings and shootings across the country in the cities of Quetta and Karachi that killed several policemen.

Pakistan charges that Jamaat-ul-Ahrar trains and plots its attacks from safe havens in Afghanistan.

Pakistani forces moved into Mohmand in 2010, seeking to impose control over the region and push out militant groups. But over the past year, Jamaat-ul-Ahrar has crept back, establishing a presence in remote parts of the region despite the military's presence.

Its fighters and leaders elude capture by moving back and forth across the border into Afghanistan's Nangarhar and Kunar provinces. The group's spokesman, Ehsanullah Ehsan, routinely calls journalists on an Afghan phone number.

Still, in an interview with The Associated Press, Ehsan denied operating out of Afghanistan.

"It is baseless that we are making plans on Afghan soil," he said in an email exchange this week.

Islamabad's accusations have further muddied the uneasy relationship between Pakistan and Afghanistan. For years, Kabul and Washington have accused Pakistan of providing refuge to Taliban leaders, especially the Haqqani group, which is routinely blamed for the worst attacks in Kabul. Pakistan denies the charge. Pakistan was one of only three countries to recognize the Taliban when they ruled Afghanistan before being ousted in 2001. Saudi Arabia and the United Arab Emirates also recognized them.

Still, Asad Munir, a retired Pakistan army brigadier and former intelligence chief in Peshawar, said Jamaat-ul-Ahrar has been weakened by military assaults on territory it controlled in Mohmand. Warrens of tunnels and hideouts that ran throughout the area have been uncovered and destroyed.

"We don't need to be scared of them," he said.

But Jamaat-ul-Ahrar has built ties with other militant factions across Pakistan, including in the country's main region Punjab, hundreds of miles from Mohmand.

Its leader, Omar Khaled Khorasani, a self-professed poet and former journalist, was once a member of the outlawed Jaish-e-Mohammed, a Punjab-based organization blamed by New Delhi for a weekend assault on an Indian military post in the disputed Kashmir region that killed 17 Indian soldiers.

Khorasani also used to write regularly for Jaish-e-Mohammed's publication, Zarb-e-Momin, which attacks the west and India, promises to impose strict Islamic Shariah laws and extols the virtues of jihad and the rewards of martyrdom, according to Munir, the former intelligence officer.

Jamaat-ul-Ahrar also has ties to the virulently anti-Shiite Muslim group Lashkar-e-Janghvi and Lashkar-e-Taiba, an anti-Indian group, said Munir.

After the U.S. last month declared the group a terrorist organization, Khorasani — whose real name is Abdul Wali Khan — made a long speech saying the group had no intention of waging attacks outside of Pakistan.

"Jamaat-ul-Ahrar doesn't attack any country or its interests other than Pakistan," he said in the speech. "We have no involvement in any militant activity on global level."