Bangkok: Islamic State-linked militants who rampaged through a southern Philippines town have threatened to kill a priest and other Christian hostages.
The threat came as thousands of civilians fled Marawi, 830 kilometres south of Manila, on Wednesday as troops fought running battles with militants who took over a large part of the city on Tuesday, flying black Islamic State flags and torching key government buildings and a church.
Philippine President Rodrigo Duterte declared that martial law he imposed across Mindanao, home to 20 million people, in response to the attacks would be "harsh" to quell the rising threat of Islamic State-inspired violence.
After cutting short a trip to Moscow, Mr Duterte also told reporters in Manila he is considering expanding martial law to other parts of the country.
"I have always said do not force my hand into it because if I start to declare martial law I will solve all the problems connected with law and order," he said.
The Catholic Church said Marawi's local priest Father Chito Suganob from the city's Cathedral of Our Lady Help of Christians and an unspecified number of church-goers were taken hostage by Maute group militants.
"They have threatened to kill the hostages if the government forces unleashed against them are not recalled," said a statement released by the head of the Catholic Bishop's Conference of the Philippines, Archbishop Socrates Villegas.
"We beg every Filipino to pray for Father Chito and for the other hostages," it said.
A military spokesman said information was being sought on the reported kidnappings.
Authorities estimated around 100 extremists had occupied the city of 200,000, while more than 1,000 troops started arriving in the area to bolster local forces at first light on Wednesday.
The military has released few details about the clashes but insisted the situation was under control.
But fleeing civilians said the parts of the city remained under control of the militants.
"They are all over the main roads and two bridges leading to Marawi," student Rabani Mautum told Reuters from a town 16 kilometres from Marawi.
"I was in school when I heard gunfire ... when we came out there were bloodstains in the building but we did not see nay dead or wounded," he said.
Mr Duterte, a firebrand native of Mindanao, has often threatened to impose martial law to crush extremists and stop radical Islamist ideology spreading since taking office in June last year, prompting concerns by human rights groups that he plans to create a dictatorship in the island nation of 100 million people.
The late dictator Ferdinand Marcos used martial law to remain in power during his two-decade reign, which ended in 1986 with a "People Power" revolution.
The 60-day martial law declaration for Mindanao will allow government forces to carry out searches and arrests and detain suspects without warrants.
The Maute group, which has hideouts near Marawi, and the brutal Abu Sayyaf group which operates across the southern Philippines, have engaged in deadly clashes with government forces over several months.
The government blamed the Maute group for a bombing in a marketplace in Mr Duterte's hometown of Davaoin September 2016 which killed 14 people and wounded dozens.
Last November, the government claimed it had killed 61 Maute fighters in five days of military air and ground assaults.
Foreign Minister Julie Bishop said in March that Australia is readying itself for the possibility of Islamic State declaring a "caliphate" in the southern Philippines as extremists are forced out of the Middle East.
"This brings the threat right to our doorstep," she said.
An estimated 600 fighters from South-east Asian nations are fighting in Syria and Iraq.
Philippine Defence Secretary Delfin Lorenzana said the clashes in Marawi erupted when security forces raided a house where they believed Isnilon Hapilon, an Abu Sayyaf commander and the claimed head of Islamic State in the Philippines, was believed to be holed up.
The US State Department has a $US5million bounty for the capture of Hapilon, an Arabic-speaking preacher known for his expertise in commando assaults, who pledged allegiance to Islamic State in 2014.
He is believed to be recovering from wounds sustained in a military strike in January.
Six weeks ago the military foiled a mass kidnapping attempt by the Abu Sayyaf on the central island of Bohol, which is popular with foreign tourists.
Earlier in May the United States warned of possible kidnappings in other parts of the country, including Cebu.
Muslim militants have been waging a rebellion since the 1970s for an autonomous homeland in Mindanao, with the conflict claiming more than 130,000 lives.
Some Muslim rebel groups are engaged in peace talks with the government.
with agencies
