Christians worldwide are being asked to pray for the people of Mindanao in southern Philippines amid the ongoing military campaign to flush out a large group of Muslim militants with links to the Islamic State (ISIS).

On Wednesday, ISIS claimed responsibility for the ongoing clashes between the Abu Sayyaf militants and Philippine soldiers that began last weekend, Reuters reports. The clashes have so far claimed the lives of at least 43 people—18 soldiers and 25 militants, official sources said.

"With the grace of god we were able to detonate seven trucks carrying soldiers," an ISIS statement picked up from Cairo, Egypt said.

Todd Nettleton, spokesman for the Voice of the Martyrs (VOM) USA, said amid the raging conflict, pastors and Christian leaders in the region are being targeted by the Abu Sayyaf and other heavily armed Muslim extremists for their evangelistic activities.

"There are threats against what they're doing. They also understand the call of the Gospel and the call of Christ is to go out and make disciples, to go out and share with unbelievers the truth of the Gospel," he said in a report filed by Mission Network News (MNN).

"Even though the leaders expect threats, that's not to say they don't get discouraged. VOM helps front-line workers by supporting theological training schools as well as pastoral conferences on overcoming persecution," he said.

Nettleton said Mindanao remains a particularly dangerous place to live for former Muslims who converted to Christianity because conversion is seen in Islam as treason.

He said Christians can help by praying for the missionaries spreading the Gospel and for the local Christian community in the Philippines, especially the new converts.

"We know that God can go where we can't go; He can provide encouragement to people we don't even know," Nettleton said.

MNN is asking Christians worldwide to pray for God's hand of protection over the people of Mindanao. "Pray especially for converts from Islam. As new believers learn to live as followers of Christ, pour into their lives grace upon grace through the preaching of God's Word," it said.

Meanwhile, Philippine government troops are closing in on more than 60 Abu Sayyaf gunmen in Tipo-Tipo, Basilan following last weekend's bloody clashes that left 18 soldiers dead and 56 wounded, the Philippine Star reports.

On Tuesday, Philippine troops captured three Abu Sayyaf militants.

"There is a very large operation going on to get the remnants of this Abu Sayyaf group," Maj. Filemon Tan Jr., designated ground operation spokesman, said.

Armed Forces of the Philippines spokesperson Brig. Gen. Restituto Padilla said the military is now using artillery fire to try and flush out the militants.

As of Tuesday, the military said 25 Abu Sayyaf militants have been killed in the last two days of fighting. One of the reported fatalities was identified as Furuji Indama, known as the right-hand man of Abu Sayyaf leader Isnilon Hapilon.

Another significant finding was that a Moroccan bomb-making instructor named Khattab was among the terrorists killed.

Philippine Defense Secretary Voltaire Gazmin confirmed the killing of Khattab, the Philippine Daily Inquirer reports.

"We lessened the risk of transferring the technology to make bombs. [In fact], he was wearing a vest lined with explosives [when his body was retrieved]," Gazmin said.

The defence chief confirmed reports that Khattab was in the Philippines "to unify all the terrorist groups here and link them with the international terrorist network."