The Syrian Democratic Forces, supported by warplanes of a US-led coalition, dislodged IS fighters from their last redoubt in the village of Baghouz near the Iraqi border on March 23, following a months-long offensive.

The US-backed alliance is now "tracking down remnants of the terrorist group", SDF spokesman Mustefa Bali said on Tuesday.

"There are groups hiding in caves overlooking Baghouz," he said.

The US-led coalition said it was supporting sweeping operations with air strikes on jihadist hideouts.

"The Syrian Democratic Forces continues to deny Daesh a physical space and influence in the area and work to deny them the resources they need to return," coalition spokesman Scott Rawlinson told AFP on Monday, using an Arabic acronym for IS.

"In support of back-clearance operations, the coalition continues to conduct precision strike support in coordination with SDF," he said.

The official said anti-IS operations are now focusing on "eroding" IS's "capacity to regenerate and collaborate".

The Syrian Observatory for Human Rights, a Britain-based war monitor, said that more than a dozen coalition air strikes have targeted IS hideouts in Baghouz since Sunday.

Strikes hit caves and farmlands in the village where holdout jihadists are believed to be hiding, it said.

IS fighters also retain a presence in Syria's vast Badia desert and various other hideouts, and have continued to claim deadly attacks in SDF-held territory.

Last week, IS killed seven US-backed fighters in an attack on a checkpoint in the northern city of Manbij, which is controlled by a local council linked to the SDF.

The Observatory on Tuesday said that nine suspected jihadists were captured in the former IS bastion of Raqa since Sunday.

The SDF has warned that a new phase has begun in anti-IS operations, following the defeat of the jihadist proto-state.

They appealed for sustained coalition assistance to help smash sleeper cells.

The "caliphate" proclaimed in mid-2014 by fugitive IS supremo Abu Bakr al-Baghdadi started collapsing in 2017 when parallel offensives in Iraq and Syria wrested back its main urban hubs -- Mosul and Raqa.

The nearly five years of fighting against the most brutal jihadist group in modern history left major cities in ruins and populations homeless.