QAMISHLI, SYRIA (REUTERS) - After months in which the United States and European countries issued warnings about their citizens travelling to Syria fight on behalf of the Islamic State in Iraq and Syria (ISIS), there are new reports of Westerners going to fight on the other side, against the militants.

A man who said he is a US citizen and former soldier from Ohio said in a video interview inside Syria that he had come to join Kurdish fighters to battle Islamic State.

Other Americans were also fighting there on behalf of a Syrian Kurdish group, said the man, who identified himself as Brian Wilson and spoke to a freelance photographer working for Reuters in Syria.

"Most people in America are against Daesh of course, Islamic State," Wilson said, sitting with four Kurdish fighters and dressed in green camouflage clothes in the northeast Syrian Kurdish city of Qamishli. Daesh is the Arabic acronym for Islamic State.

"There are a few Americans who wanted to come here and help the YPG in any way we can," he said, referring to the main Kurdish group fighting against Islamist militants in Syria.

Wilson is the second American known to have joined the YPG forces. Jordan Matson, a 28-year-old from Wisconsin, is also fighting with the YPG, a spokesman for the armed group said last week. He has given an interview to a Kurdish TV station.

ISIS tightened its siege of the YPG-held Syrian Kurdish town of Kobani on Tuesday despite US-led air strikes meant to weaken the group. The fighting has sent more than 180,000 refugees into Turkey since last month.

The United States has been striking ISIS targets in Iraq since August and extended the campaign to Syria in September.

Washington is supplying weapons to Kurdish fighters in Iraq to help them battle Islamic State, but does not have an official policy of helping Kurdish groups in Syria.

Wilson, who looked middle aged and had his head shaved, said he met YPG fighters through "Kurdish contacts". He said he had not yet engaged in combat.

"Everything has been fine. They're very nice, very accommodating, hospitable. Very good people," he said of his hosts.

Western countries say scores of their citizens have travelled to Syria to fight on behalf of ISIS, a phenomenon hammered home in videos showing the beheadings of hostages apparently by a fighter with a British accent.