The battle for the Islamic State group's de facto Syria capital, Raqqa, has reached its "final stages," the Syrian Democratic Forces said Wednesday, almost four months after the U.S.-backed force launched an assault on the self-proclaimed capital of the militant group.

The Kurdish-led Syrian Democratic Forces said it captured Raqqa's last grain silos from the militants in a surprise offensive on the city's northern neighborhoods, mounted five days ago. Less than 300 militants remain holed up in the city, which has witnessed an intense bombing campaign, particularly in the last few days, according to the head of the Britain-based Syrian Observatory that monitors the war.

The campaign to take Raqqa began in June in a quick advance after a breach of the wall of the Old City, a major fortification for the militants. But it has since slowed down as the forces faced mounting resistance from the militants.

Three months after the Raqqa campaign began, the SDF began a separate campaign earlier this month to take the other IS stronghold in Syria, Deir el-Zour.

Fighters from Syrian Democratic Forces (SDF) stand Fighters from Syrian Democratic Forces (SDF) stand near destroyed Uwais al-Qarni shrine in Raqqa, Syria, Sept. 16, 2017. Fighters from Syrian Democratic Forces (SDF) stand near destroyed Uwais al-Qarni shrine in Raqqa, Syria, Sept. 16, 2017.

The SDF's campaign for oil-rich Deir el-Zour province, which straddles the border with Iraq, is caught up in a race with Syrian government forces and allied troops, who are also vying for control.

In the past two weeks, the pro-government forces, backed by Russian air cover and Iranian-allied militia, gained control of most of the city of the same name and crossed over the Euphrates River to the area of operations of the SDF.

Coalition and SDF officials say they want to avoid clashes with pro-Syrian government forces, which crossed to the eastern side of the river earlier this week, bringing them just kilometers away from SDF forces.

An SDF commander in Deir el-Zour told The Associated Press his troops have redirected their battles away from the river for now to fight IS militants deeper in the eastern desert. He said with the Raqqa battle nearing an end, he hopes troops fighting there would come to boost his ranks.

"We hope that the SDF fighting in Raqqa, including our own fighters taking part in Raqqa, finish there so they can come and boost our advance on the eastern bank of the river," said Ahmed Abu Khawla, the commander of the SDF unit Deir el-Zour Military Council, which is leading the fight on the oil-rich province.

Meanwhile, the U.S. and its international coalition partners intensified their air raids on the militants' last remaining enclave in Raqqa, according to the Observatory. The U.S. also has hundreds of forces embedded with the Syrian fighters who provide artillery fire and other support.

Observatory director Rami Abdurrahman said there are less than 300 remaining in an enclave in Raqqa, which is now 90 percent controlled by the SDF.

Civilians trapped, killed

The Observatory on Wednesday accused the U.S.-led coalition of killing more than 1,000 civilians in airstrikes on Raqqa since the SDF first entered the city in June. The claim could not be independently verified. The coalition has said repeatedly that it relies on the latest intelligence to minimize civilian casualties and strike only military targets.

FILE - Fighters from Syrian Democratic Forces walk Fighters from Syrian Democratic Forces (SDF) walk together along a damaged street in Raqqa, Syria, Sept. 16, 2017. Fighters from Syrian Democratic Forces (SDF) walk together along a damaged street in Raqqa, Syria, Sept. 16, 2017.

Thousands of civilians are believed trapped in the militants' enclave in the north of the city as human shields, according to the SDF.

Tens of thousands more have been displaced by the fighting since June, often to wind up in abject conditions in SDF-run camps in northern or eastern Raqqa.

The Kurds leading the battles say they want their own autonomous zone in a federated Syrian republic. They operate independently of the Damascus-based Syrian government, which is supported by Russia and Iran.

Islamic State control

Meanwhile, the fighting in Deir el-Zour is largely concentrated around the provincial capital, which lies 125 kilometers (78 miles) southeast of Raqqa, on the banks of the Euphrates River.

IS still controls broad swathes of eastern Syria and pockets of territory in neighboring Iraq.

Abu Khawla, the SDF commander, said his troops have moved away from the Euphrates river to the east, deeper into eastern Deir el-Zour to clear areas behind them of IS militants.

"There is tension ... there are consultations between the Russians and the coalition. We don't deny this," said Abu Khawla. "But we have a major plan to liberate all the eastern side of the river."

Abu Khawla said his forces are now close to the town of al-Sour to the east, and aim to sever the militants' supply lines from al-Mayadeen, a town farther south, where IS leaders are believed to have congregated amid the multiple campaigns against the group.