Move follows similar commitment from US as many stranded in heat without food or water try to escape Isis militants

France has announced it will send arms to the Kurds and ethnic Yazidis in Iraq immediately, to help them defend their territory against Islamic State extremists.

The announcement by President François Hollande's office came as the US said it was also stepping up its role. The Pentagon will send 130 more military advisers – marines and special operations troops – to northern Iraq to assess the humanitarian crisis.

It is believed their main goal is to organise a land escape route for up to 30,000 civilians, mostly of the Yazidi religious minority, who remain trapped on Mount Sinjar near the Syrian border, hemmed in by Islamic State (Isis) militants who have threatened to kill them.

"In order to respond to the urgent need expressed by the Kurdistan regional authorities, the president has decided, in agreement with Baghdad, to deliver arms in the coming hours," Hollande's office said in a statement. "France intends to play an active role by providing, along with its partners and in liaison with the new Iraqi authorities, all the assistance required."

David Cameron meanwhile cut short his holiday in Portugal by a day to return to Downing Street to decide on further steps the UK could take to assist the Kurds and the Yazidis. Britain is already airlifting Jordanian military vehicles to Kurdistan and taking part in air drops on Mount Sinjar.

US special forces are already thought to be working with Kurdish peshmergafighters to help thousands of the besieged Yazidis to walk off the mountain, but many of the civilians remain trapped or are unable to make the trek after 11 days on the barren mountainside with little food or water.

The US and UK have been dropping supplies in recent days from military transport planes, and the Kurdish authorities have also flown in supplies on a handful of helicopters risking ground fire from Isis, and taking stranded Yazidis out a dozen at a time. Those that remain on the mountain face death from hunger or thirst and a constant threat from Isis, without a land escape route.

UN minority rights expert Rita Izsak has warned they face "a mass atrocity and potential genocide within days or hours". The US secretary of state, John Kerry, said that Washington is looking at options to bring the trapped civilians out. "We will make a very rapid and critical assessment because we understand it is urgent to try to move those people off the mountains," he said.

Kieran Dwyer, a spokesman for the UN office for the co-ordination of humanitarian affairs, said "It's really hot up on the mountain. It's pushing 45 degrees [C] in the shade, and there is very little shade up there. The people are really exposed, and they ran there quickly without taking much with them, so they are in a really tough situation."

Dwyer, speaking from Irbil, the main city in Kurdistan, said that the Yazidis were spread over multiple locations across the bare mountain. Those towards the north had a means to walk towards Syria to escape, but he said the walk of at least seven hours was gruelling and dangerous as militants could reach part of the route. Those on the south side were more completely hemmed in by Isis militants.

Meanwhile, Iran's leader, Ayatollah Ali Khamenei, added to the intense international pressure on the beleaguered Iraqi prime minister, Nouri al-Maliki, to step down to make way for his designated successor, Haider al-Abadi, saying he hoped Abadi's appointment would "untie the knot" of Baghdad politics and lead to the formation of a new government.

The deadlock in Iraqi politics is generally believed to have created the conditions for the spread of Isis. Maliki however showed no sign of stepping down on Wednesday, saying Abadi's appointment violated the constitution and "had no value". In a televised speech, Maliki said everyone should accept a pending federal court ruling on an objection he filed against Abadi's appointment, and said his government would continue until a final decision was made.