The US-backed Syrian Democratic Forces (SDF) began an assault against the final ISIS extremist group enclave in eastern Syria on Saturday, aiming to wipe out the last vestige of the extremist group’s “caliphate” in the SDF’s area of operations.

President Donald Trump, who is planning to pull US forces out of Syria, said on Wednesday he expected an announcement as early as next week that the US-led coalition operating in support of the SDF had reclaimed all the territory previously held by the extremist group.

The enclave, close to the Iraqi border, comprises two villages. ISIS also still has territory in the part of Syria that is mostly under the control of the Russian- and Iranian-backed Syrian government.

Mustafa Bali, head of the SDF media office, told Reuters the aim of the assault was to “eliminate the last remnants of the terrorist organization” and called it the “last battle”.

He later wrote on Twitter that the battle had started and the enclave would “be cleared soon”.

Bali told Reuters that in the last 10 days SDF fighters had handled the battle “patiently” as more than 20,000 civilians were evacuated from the besieged enclave.

The SDF, spearheaded by the Kurdish YPG militia, has driven ISIS out of a swathe of territory in northern and eastern Syria over the last four years.

ISIS leader Abu Bakr al-Baghdadi declared the group’s “caliphate” in 2014 in territory stretching across Iraq and Syria. But the group lost its two main prizes - the Syrian city of Raqqa and Iraq’s Mosul - in 2017.

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

The remaining ISIS territory in Syria is west of the Euphrates.

Trump said in December he was pulling all 2,000 U.S. troops out of Syria, saying the battle against ISIS there was almost won.

But a top US general said on Tuesday the group would pose an enduring threat following the US withdrawal, as it retained leaders, fighters, facilitators and resources that would fuel a menacing insurgency.

The Wall Street Journal reported on Friday that the US military was preparing to withdraw from Syria by the end of April.

A US official confirmed that target date to Reuters, saying the withdrawal included a pull-out from the US military base at Tanf, near the Syrian border with Iraq and Jordan.