Christians are being used as human shields by ISIS militants in the Philippines' as government forces try to recapture Marawi City.

The jihadist fighters seized the town five weeks ago and those who remain are being used as sex slaves or killed, according to the MailOnline.

Among the hostages is Father Teresito Soganub, a leading church figure, who authorities believe is being held alongside more than 100 other Christians.

'They are being forced to be sex slaves, forced to destroy the dignity of these women,' said army spokesman Jo-Ar Herrera.

'This is what is happening inside, this is very evident...these are evil personalities.'

Abdullah Maute, one of two brothers who lead the terrorist splinter group, said he would release Soganub in return for the release of his parents who are held by the government.

But Philippine President Rodrigo Duterte refused the offer, saying he would not not bargain with terrorists.

Heavy fighting continued on Tuesday with airstrikes ordered on the shrinking rebel-controlled area.

An government spokesman said: 'Let us remind the public, the gravity of the terrorists and their supporters' offences is immense and they must be held accountable for all their actions.'

Now entering its second month, the length of the seize is causing concern about the strength of the jihadists in the mainly Catholic southern Philippines.

Despite a sustained bombing campaign from President Duterte's armed forces, the Islamists have a grip on the city and most of the 200,000 inhabitants have fled.

Some 70 servicemen, 27 civilians and 290 militants have since been killed and 246,000 people have been displaced from a town where some neighbourhoods have been reduced to rubble, according to the MailOnline.