WASHINGTON • United States President Donald Trump has signed an executive order giving the military 30 days to devise a plan to "defeat" the Islamic State in Iraq and Syria (ISIS).

The move makes good on a key campaign pledge of Mr Trump, who mocked the slow progress made by his predecessor Barack Obama in the fight against the militant group.

The text signed on Saturday, which calls for a "comprehensive strategy and plans for the defeat of ISIS", is seen as meaning that more US forces and military hardware will move into Iraq and Syria.

Under the order, Pentagon chief James Mattis has also been tasked with recommending changes to US rules of engagement and policy restrictions to eliminate those that "exceed the requirements of international law regarding the use of force against ISIS". The order seeks to cut the group's financial support as well.

Mr Trump and Russian counterpart Vladimir Putin agreed during a telephone call to establish "real coordination" against ISIS in Syria, according to the Kremlin.

Yet, many in the US military are wary of Russia's role in Syria, with Moscow seen as seeking first and foremost to support and defend President Bashar al-Assad's regime.

"We have to get rid of ISIS. We have no choice," Mr Trump told Fox News in an interview broadcast on Thursday. "This is evil. This is a level of evil that we haven't seen."

Mr Obama took a longer-term view of the fight against ISIS, with a more cautious commitment of US forces while ramping up an air war against the extremists.

"President Trump might be looking for something with quicker results, that could put some more options on the table," retired Lieutenant-General David Barno, who led coalition forces in Afghanistan from 2003 to 2005, told National Public Radio last Friday.

The US currently has 5,000 troops in Iraq and 500 in Syria as "advisers" - but also artillery and aircraft to help in the fight.

They have provided substantial support to the assault led by Iraqi forces to break the group's hold on the key city of Mosul.

The slow, steady assault has driven ISIS fighters out of part of the city on the east bank of the Tigris River, and forces are now preparing an assault on ISIS-held Mosul neighbourhoods on the west bank.

According to reports, an escalation of the US role could involve more American armour and helicopters engaging in assaults on ISIS positions together with Iraqi, Turkish and Kurdish forces.

Mr Trump "could elect to put American boots on the ground in larger numbers", said Lt-Gen Barno. "That all entails new uses of military power... and that opens the prospect of a deeper involvement, with more casualties."

AGENCE FRANCE-PRESSE