Foreign ministers from 68 countries are meeting in Washington, DC, to agree on the next steps to defeat ISIL, the first such gathering of the US-led military coalition since the election of President Donald Trump in November.

US Secretary of State Rex Tillerson and Defense Secretary Jim Mattis are hosting Iraq's prime minister and diplomats from the coalition partners in a two-day meeting at the state department starting on Wednesday.

Trump has vowed to make the fight against Islamic State in Iraq and the Levant (ISIL, also known as ISIS) a priority and directed the Pentagon and other agencies in January to submit a plan for defeating the group.

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ISIL has been losing ground in both Iraq and Syria, and three separate forces, backed by the United States, Turkey and Russia, are advancing on the group's Syrian stronghold of Raqqa.

The meeting is the first of the international coalition since Iraqi government forces, backed by the US-led international coalition, retook several Iraqi cities, including eastern Mosul, from ISIL last year.

While the armed group is overwhelmingly outnumbered by Iraqi forces, it has been using suicide car bombs and snipers to defend its remaining strongholds.

Iraqi Prime Minister Haider al-Abadi, who met Trump in Washington on Monday, said he had won assurances of more US support in the war against ISIL.

A White House statement after the meeting said both Trump and Abadi agreed that "terrorism cannot be defeated by military might alone". The two leaders also called for deepening commercial ties.

Discussions on Wednesday will also focus on how to help Mosul rebuild and ways to tackle ISIL operations in Libya and elsewhere.

In Syria, the US-led coalition has been working with an alliance of Kurdish and Arab militias. Its current focus is to encircle and ultimately recapture Raqqa - ISIL's main base of operations in Syria.

The Syrian Democratic Forces (SDF), a Kurdish-led group of militias backed by the US-led coalition, is fighting to isolate Raqqa before an anticipated assault on the city, which the ISIL group has used as a command node to plan attacks abroad.

In a statement put out on social media on Wednesday, the SDF said the US-coalition has air-dropped US and SDF forces near the town of Tabqa in Raqqa province, expanding its campaign against ISIL in the area.

The operation aims to both capture the strategic area of al-Tabqa, just 45km west of Raqqa, and to curb Syrian government advances in that direction.

"What we’re seeing right now is a race to Raqqa. Which forces are going to try to take on ISIL in that pivotal city? Is it going to by Syrian forces backed by Russia and Iran, or is it going to be US forces? Another big question is what role is Turkey going to play in all of this?" said Al Jazeera's Patty Culhane, reporting from the US capitol.

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"This could be an indication though that this key offensive that we’ve been waiting for is going to get under way."

Pentagon spokesman Eric Pahon described the operation as a large, high-priority offensive to secure the area around Tabqa and the associated Tabqa Dam on the Euphrates.

"This is a significant strategic target," he said. If successful, the operation would "basically cut ISIS off" from the western approaches to Raqqa.

The head of the YPG militia, the strongest in the SDF, said last week that the offensive to retake Raqqa would begin in early April, but a spokesman for the Pentagon said no decision had yet been made.

Syrian President Bashar al-Assad, who is supported by Russia and Iran, has said he saw scope for cooperation with Trump, although he has dismissed the US-backed military campaign against ISIL in Syria as "only a few raids".