Philippines President Rodrigo Duterte has been given the green light to move ahead with his plans to extend martial law to the southern part of the country.

The Philippine Congress voted overwhelmingly (261-18) in favour of the extension to tackle the military insurgency of Isis-affiliated rebel groups on Saturday (22 July).

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The vote allows Duterte to use the military to enforce law on the island of Mindanao, parts of which, such as Marawi, have been besieged by militants pledging allegiance to Isis.

The president asked congress to approve his request to extend a proclamation which placed Mindanao under martial law for two months.

The proclamation, which was due to expire on Saturday, was extended as troops struggled to contain a rebellion by Islamist militants in the city of Marawi. Since fighting broke out in the city on 23 May, at least 428 militants, 105 soldiers and policemen, and 45 civilians have been killed.

The law will now remain in effect until 31 December.

The president's spokesperson Ernesto Abella said that the "extension of martial law is essential to overall peace and stability."

"We want to stop the spread of evil ideology of terrorism and free the people of Mindanao from the tyranny of lawlessness and violent extremism," he said in a statement.

Duterte says martial law is necessary to deal with the Islamist insurgency, but his critics accuse him of trying to seize more power.

Martial law was previously imposed in the Philippines by late dictator Ferdinand Marcos, whose regime was infamous for its brutality and corruption. Marcos was ousted in a "people power" revolt in 1986.

"I fear that the plan to extend the martial law in Mindanao will pave the way for a Philippines-wide martial law," Senator Risa Hontiveros told AFP.

Congressman Edcel Lagman said there was "no factual basis" for the extension.

"Extending martial law can unmask the Duterte government's real political intentions to apply authoritarian rule in the country, like the way he ruled Davao City for 20 years as a city mayor," said Rommel Banlaoi, chairman of the Philippine Institute for Peace, Violence and Terrorism Research.

"Duterte's martial law threatens military abuses in Mindanao that could rival the murderous 'drug war' in urban areas," Human Rights Watch director for Asia Phelim Kine said after the Philippine congress first imposed martial law.

Since becoming president, Duterte has fulfilled his election pledge to crack down on the drugs epidemic plaguing his country. His brutal war on drugs has claimed thousands of lives.

Philippines Isis