WASHINGTON — The United States is sending an additional 400 troops to Syria to help prepare for the looming fight for Raqqa, the capital of the Islamic State’s self-proclaimed caliphate, American officials said on Thursday.
The increase, which includes a team of Army Rangers and a Marine artillery unit that have already arrived in the country, appears to represent a near-doubling of the number of American troops in Syria.
The United States military had declined to say precisely how many troops it had deployed in the country. The formal troop cap for Syria is 503, but commanders have the authority to temporarily exceed that limit to meet military requirements.
The presence of the Rangers became apparent last weekend when they were seen driving around the northern Syrian town of Manbij in Stryker vehicles and armored Humvees. The Washington Post earlier reported the deployment of the Marine artillery battery.
“We are preparing logistical and fire support to enable a successful assault on Raqqa, the self-proclaimed capital of ISIS,” said Col. John L. Dorrian, a spokesman for the American-led command that is fighting the Islamic State in Iraq and Syria.
“The exact numbers and locations of these forces are sensitive in order to protect our forces, but there will be approximately an additional 400 enabling forces deployed for a temporary period to enable our Syrian partnered forces to defeat ISIS in Raqqa,” Colonel Dorrian added.
“Our indigenous partners in Syria face an entrenched foe and like the Iraqis, will require additional support to enable them to fight and defeat ISIS in Raqqa,” he said.
The mission of the additional troops will be to help Syrian fighters prepare for the offensive on Islamic State forces in Raqqa. They will provide artillery support, training and protection for improvised explosives, among other efforts, Colonel Dorrian said.
The decision to deploy artillery mimics the approach taken in Mosul, Iraq, where American and French artillery have been supporting the Iraqi offensive to take the western half of the city.
In the case of Raqqa, the idea is that Syrian forces will do the bulk of the fighting on the ground but that Americans will assist them by providing advisers as well as firepower.
The United States is already carrying out airstrikes in Syria and has deployed surface-to-surface rockets in the northern part of the country. Before he left office, President Barack Obama approved the use of a small number of Apache attack helicopters, and they are expected to be part of the Raqqa operation, as well. Now, Marine artillery is being added to the mix.
The Trump administration, however, has yet to make clear which fighters will seize Raqqa. American military commands favor a mixed force of Syrian Arabs and the Kurdish Y.P.G. militia. But Turkey has objected to arming the Kurds, since it has denounced the group as terrorists.
Gen. Joseph L. Votel, the head of the United States Central Command, alluded to the need for the reinforcements during a recent visit to the Middle East.
“I am very concerned about maintaining momentum,” he told reporters accompanying him on a trip to the region.
General Votel is scheduled to testify to the Senate Armed Services Committee on Thursday morning about the situation in Syria and plans to fight the Islamic State.
Gen. Thomas D. Waldhauser, who heads the Africa Command, will also appear before panel. Among other duties, the Africa Command has responsibility for operations in Libya and North Africa.