WASHINGTON (Reuters) - The top American commander in Iraq believes U.S.-backed forces will recapture Islamic State’s two major strongholds - the cities of Raqqa in Syria and Mosul in Iraq - within the next six months, his spokesman said on Wednesday.

The spokesman, Air Force Colonel John Dorrian, confirmed reported remarks by U.S. Army Lieutenant General Stephen Townsend.

Townsend was quoted as telling the Associated Press that “within the next six months I think we’ll see both (the Mosul and Raqqa campaigns) conclude.”

The latest word on the fight against Islamic State came as the U.S. military was developing a plan at President Donald Trump’s request to accelerate the campaign to defeat the militant group. The plan is due late this month.

While it has lost some territory in Mosul, Islamic State still holds swaths of Syrian territory and is putting up fierce resistance in Raqqa, the militant group’s de facto capital in eastern Syria, where U.S. officials believe is the hub for its plots for attacks against Western targets.

Experts said the Pentagon could still request some additional forces. Less than 6,000 American troops are currently deployed to both Iraq and Syria.

But they also said the Pentagon may focus on other options, like increasing the number of attack helicopters and air strikes and bringing in more artillery. The military may also seek more authority to make battlefield decisions, allowing commanders to take advantage of opportunities more quickly.

Among the big policy decisions awaiting the Trump administration before any U.S.-backed offensive against Raqqa is whether to arm Kurdish fighters who NATO ally Turkey accuses of being terrorists.

“It is very tricky because how do you engage the Turks and the Kurds at the same time and keep them from fighting each other?,” said Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy.

Anthony Cordesman, a defense expert at the Center for Strategic and International Studies think tank in Washington, warned that predicting the length of the battle at this point was extremely difficult.

“Frankly with the situation in Raqqa, the situation is so uncertain that there is no way to make a prediction,” Cordesman said.

SHRINKING CALIPHATE

U.S. Defense Secretary Jim Mattis and his Iraqi counterpart spoke by phone for the first time on Wednesday and discussed “planning for operations to liberate western Mosul,” the Pentagon said.

Islamic State in recent months has been weakened on many fronts, with its territory in parts of Iraq and Syria shrinking.

In Iraq, Islamic State has lost territory in and around its northern stronghold of Mosul since U.S.-backed Iraqi forces last October began the biggest ground operation in the country since the 2003 U.S.-led invasion that toppled Saddam Hussein.

The group holds around 90 percent of the Syrian province of Deir Ez-Zor near the Iraqi border, along with Raqqa and some parts of the eastern countryside of Aleppo in northern Syria. It also controls Palmyra and some pockets in Deraa in the south.

Dorrian, speaking earlier to Pentagon reporters, said he expected U.S.-backed forces on the ground in Syria to nearly isolate Raqqa in coming weeks, setting the stage for a push to seize the city.

“What we would expect is that within the next few weeks is that the city would be nearly completely isolated and then there will be a decision point to move in,” Dorrian said.

U.S. military leaders have warned that Islamic State will likely turn into a more classic insurgency once it loses Raqqa and Mosul, meaning the broader fight could stretch on for years.