Baghdad: Washington was set on Thursday to approve plans to train and arm Syrian rebels in the fight against the Islamic State of Iraq and the Levant (Isil) as the Islamist militants gained ground in the north of the country.

Fears grew over the wide reach of Isil, which has seized large parts of Iraq and Syria, after Australia said it foiled a plot by group members to kidnap and behead random members of the public.

The US Senate was expected to back a plan, approved by the House of Representatives on Wednesday, to train and equip moderate rebels in Syria, a key part of the anti-Isil strategy.

Who exactly will benefit from the programme is unclear, as the rebels battling President Bashar Al Assad lack a clear command structure and range from secular nationalists to Al Qaida-backed extremists.

But President Barack Obama hailed the House approval as “an important step forward”, and Senate leaders are confident it will pass Thursday for his signature.

Obama met military commanders on Wednesday and, in a speech at MacDill Air Force Base in Florida, insisted the militants will be defeated.

“Our reach is long. If you threaten America, you will find no safe haven. We will find you eventually,” Obama said, also standing firm on his pledge that a US ground combat mission is not on the cards.

On Thursday a monitoring group said Isil fighters had seized a string of villages as they closed in on Syria’s third-largest Kurdish town of Ain Al Arab.

“In the past 24 hours, Isil fighters have launched a huge offensive and seized at least 16 villages to the east and west of Kobane,” said Syrian Observatory for Human Rights head Rami Abdel Rahman, using the Kurdish name for Ain Al Arab.

“Isil is using heavy weaponry, its artillery and tanks,” he said, adding that thousands of Kurdish fighters defending the town on the Turkish border were being encircled.

The US estimates that Isil has 20,000 to 31,000 fighters, including many foreigners, and there are concerns that returning militants could carry out attacks in Western countries.

The US has carried out 174 air strikes in Iraq since early August, but the mission has since expanded to areas near Baghdad for the first time.

Pro-government forces have been engaged in fierce fighting around Baghdad, with special forces widely recognised as the best in the country tackling Isil militants near the capital.

The combination of local forces and US air power seems to be having some success, apparently forcing top Isil leaders to cross the border back into Syria, the organisation’s main base.

Activists said on Wednesday that Isil fighters in Syria’s Deir Ezzor province near Iraq had abandoned some bases and redeployed their forces in anticipation of the expanded US strikes.