BEIRUT (REUTERS) - Islamic State in Iraq and Syria (ISIS) has stepped up guerrilla attacks against US-backed fighters in eastern Syria, pointing to the threat the extremists will pose even after they lose their last enclave there, the Syrian Democratic Forces (SDF) said on Tuesday (Feb 19).

The US-backed SDF is on the brink of defeating ISIS in its last pocket in eastern Syria, the village of Baghouz, where it estimates a few hundred ISIS fighters and about 2,000 civilians are under siege.

ISIS militants have intensified attacks away from the last front line in recent days, Mustafa Bali, head of the SDF media office, said.

ISIS launched two of the attacks three days ago in the village of Dhiban, 90km north of Baghouz.

In the first attack, an ambush, two SDF fighters and a militant were killed. In the second, carried out that evening by a group of foreign militants, the SDF killed three militants and captured two, Bali said.

"Sleeper cells are on the move on a daily basis," Bali said.

"The organisation (ISIS) is working on security operations in an intensive way... It is still strong, ending its military presence does not at all mean the elimination of Daesh (ISIS)," he said.

ISIS redrew the map of the Middle East in 2014 when it declared a "caliphate" across large areas of Syria and Iraq. But the group steadily lost ground and its two main prizes - the Syrian city of Raqqa and Iraq's Mosul - fell in 2017.

Spearheaded by the Kurdish YPG militia, the SDF has been the main US partner in Syria and has driven ISIS out of swathes of the north and east over the last four years.

After capturing Raqqa, the SDF advanced south into Deir al-Zor province, attacking the extremists in territory on the eastern bank of the Euphrates River.

ISIS still has some territory west of the Euphrates in a remote area otherwise controlled by the Syrian government and its allies.

SDF commander Mazloum Kobani has called for some international forces to remain in Syria to help fight ISIS and expressed hope that the United States would halt plans for a total pullout.

US President Donald Trump's withdrawal order has been criticised by allies at home and abroad.