AMMAN (Reuters) - Syrian Arab rebels have been told by Washington that new weapons were on their way to help them launch a joint offensive with their Kurdish allies on the city of Raqqa, held by Islamic State fighters, a spokesman for the rebels said on Monday.

"We met the Americans and this has been approved and we have been told these new arms, including qualitative weapons, are on their way," said Abu Muazz, a spokesman for the Raqqa Revolutionaries Front, a grouping of mainly Arab tribal insurgents who are mostly drawn from the Raqqa area.

The Arab fighters are part of a new alliance including the Kurdish YPG militia which was announced on Monday, under the banner of the Democratic Forces of Syria. The YPG militia, backed by Arab rebels, drove Islamic State from wide areas of northern Syria earlier this year.

(Reporting by Suleiman Al-Khalidi; Editing by Dominic Evans)