In the wake of more brutality by militant group Islamic State, Franklin Graham has said that even they will one day bow to Jesus.

In a Facebook post on Tuesday, Graham, president of the Billy Graham Evangelistic Association and Samaritan's Purse, wrote: "The evil of ISIS really shouldn't shock us – it is fully in keeping with their ultimate agenda of hastening a final apocalypse. God's Word tells us that there will be a final battle one day, but it will result in the defeat of Satan and all those allied with him.

"One thing is for sure – one day every knee will bow and every tongue will confess that Jesus Christ is Lord, to the glory of God the Father."

Graham highlighted the video released by IS on Sunday showing the beheading of 21 Coptic Christians in Libya, as well as the fatal shootings in Denmark over the weekend by a gunman suspected to have been inspired by the Charlie Hebdo massacre in Paris.

The evangelist criticised President Obama for failing to "acknowledge the truth and call Islamic extremism what it is."

"After a weekend of terrorism in Libya and Denmark, beginning today the White House is hosting a three-day "Summit on Countering Violent Extremism." I am perplexed as to why our President will not acknowledge the truth and call Islamic extremism what it is," Graham wrote.

"In a statement the White House even called the 21 Christians who were beheaded 'Egyptian citizens,' refusing to identify them as Christians. The truth is--their barbaric murderers openly said they killed them because they were 'people of the cross.' Why is the President seemingly continuing to protect Islam and refusing to open his eyes to the truth?"

On Monday, Graham posted a statement to his Facebook page warning that "the storm is coming".

"Can you imagine the outcry if 21 Muslims had been beheaded by Christians? Where is the universal condemnation by Muslim leaders around the world?" he asked.

"As we mourn with the families of those 21 martyrs, we'd better take this warning seriously as these acts of terror will only spread throughout Europe and the United States. If this concerns you like it does me, share this. The storm is coming."

Graham has previously encouraged Muslims to turn from Islam and accept Christ.

In a live panel interview on Fox News in January, he said: "I want to say something to all the Muslims that may be watching this that are confused and are afraid themselves. I want them to know that God loves them and that Jesus Christ died for their sins – and Christ will forgive them and heal their hearts.

"And they don't have to die in a jihad, they don't have to kill somebody else to please God. God loves them and he will accept them through faith and through his son, Jesus Christ."

In an interview with Christian Today in December, he said Islam is "a religion of war".

Extremist groups such as Islamic State and Boko Haram have not "hijacked" the religion, he added. "This is Islam. It has not been hijacked by radicals. This is the faith, this is the religion. It is what it is. It speaks for itself."