Washington (AFP) - The United States turned up the heat on the Islamic State group Thursday, sending an additional 400 US troops into Syria to support an offensive to retake Raqa, the jihadists' de facto capital.
The administration also announced a high level meeting on March 22 of the 68 countries in the US-led coalition to discuss plans to accelerate IS's defeat.
The announcements in Washington come as US-backed forces tighten their hold around jihadist bastions in Iraq's northern city of Mosul and in Raqa.
More than two and a half years after the start of a US air war against IS, the jihadists are under siege in western Mosul, abandoned to their fate by IS leader Abu Bakr Al-Baghdadi.
And a US-backed coalition of Arab-Kurdish fighters are closing in on Raqa, maneuvering to isolate the city from the rest of Syria's jihadist-controlled territory.
But the battle there is not yet won, and the Pentagon wants to make sure that the city of 300,000, a onetime propaganda showcase for IS, falls.
Among the additional US troops deployed in Syria is a Marine Corp artillery battery equipped with 155mm howitzers, according to the Pentagon.
- Options before Trump -
A US military spokesman on Thursday said that the extra troops were "temporary," and their deployment would not lead to a long-term increase in American troop levels in Syria.
But the movement comes as President Donald Trump weighs options for an intensified anti-IS campaign.
US media reports say the Pentagon is proposing the deployment of additional special operations forces, artillery and attack helicopters in support of an offensive by local ground forces.
Complicating the US strategy is the fact that NATO ally Turkey is dead set against Raqa falling to an Arab-Kurdish force grouped under the Syrian Democratic Forces.
Trained and advised by US special operations troops, the SDF has proved to be the most reliable US ally on the ground in Syria, and the only local force it considers capable of rapidly taking Raqa.
But Turkey regards the SDF as a cover for the Kurdish YPG militia, branded as a terrorist organization by Ankara.
Asked about the impasse at a hearing Thursday of the Senate Armed Services Committee, the top US commander in the region, General Joseph Votel, acknowledged that tensions between Ankara and the Kurds are near breaking point.
The chairman of the Joint Chiefs of Staff, General Joseph Dunford, has made two recent trips to Turkey to sort out the impasse.
"We are trying to take actions to prevent that from occurring," Votel told Republican Senator John McCain.
- 'Train wreck' -
Efforts have been made to address the issue at a military level, "and there has to be an effort at the political level to address this," he added.
But McCain questioned whether the Trump administration recognized the seriousness of the situation, or how important Turkish cooperation is to US efforts to retake Raqa.
"Unless something changes, I foresee a train wreck here," he said.
The Syrian dossier is not the only military issue on the Trump administration's front burner.
Votel said US troop levels in Afghanistan need to be increased, after years of a declining US military presence in the country.
More American troops were needed to break the stalemate between the Afghan government and the Taliban, he explained.
There are 8,400 US troops in the country, including counter-terrorism forces fighting Al-Qaeda and IS outside the NATO mission there.
In passing, Votel reaffirmed the US military's support for a key element of Barack Obama's military strategy: relying on indigenous forces to do the fighting, while keeping US troops in an advisory and support role.
"While this approach does present some challenges and can be more time consuming, it is proving effective and is likely to pay significant dividends going forward," he said.