US 'mechanised forces' to control Syria oil fields: Esper

The US is to use "mechanised forces" -- armoured vehicles which can include tanks -- to help control Syrian oil fields and prevent Islamic State (IS) group fighters seizing them, Defence Secretary Mark Esper said Friday.

He declined however to give any more details of the mission, which follows the abrupt withdrawal of US forces in northern Syria this month on orders from President Donald Trump.

US commanders are "considering how we might reposition forces in the area in order to make sure we secure the oil fields," Esper said, echoing an earlier Pentagon statement.

"It will include some mechanised forces -- again I'm not going to get into the details -- but the mission in Syria remains what the mission in Syria began with: it's always been about defeating the ISIS coalition," he said, referring to IS.

The shift of US forces in Syria came after Trump on Thursday tweeted: "We will NEVER let a reconstituted ISIS have those fields!" US media, including Newsweek, citing anonymous US officials, reported the Pentagon was looking at sending as many as 30 Abrams tanks and an unspecified number of soldiers to Al-Tanf, a northeast Syrian town where there is already a garrison of US troops.

While US forces have been in control of the Syrian oil fields for some time, there was a question mark over their security after Trump's order pulling US troops away from the border with Turkey.

That order opened the way for Turkey to go ahead with a long-threatened military operation to enter Syria to quash Kurdish militia in the zone who had been fighting IS.

Ankara views the militia as "terrorists" threatening its territory.

Although NATO is not involved in Syria, both the US and Turkey are member states, and the issue dominated the two-day defence ministers' meeting in Brussels -- especially as Turkey has struck a deal with Russia to patrol a "safe area" it wants set up inside Syria.

Esper said after the meeting that the US remained in contact with the Kurdish militia in Syria, and that they had managed to "recollect" dozens of IS prisoners who had escaped during the Turkish assault.