A fourth US citizen has been arrested in the greater New York area in less than a week on allegations of supporting the so-called ’Islamic State of Iraq and the Levant’ (ISIL) terrorist group.

A fourth US citizen has been arrested in the greater New York area in less than a week on allegations of supporting the so-called 'Islamic State of Iraq and the Levant' (ISIL) terrorist group.

Samuel Rahamin Topaz, 21, from Fort Lee, New Jersey, was charged with conspiracy to provide material support to ISIL.

He faces 15 years in prison if convicted and was remanded without bail after being arrested at home on Wednesday, prosecutors said.

Court papers allege he was in close contact with Munther Omar Saleh, a 20-year old student from New York who was arrested last Saturday after trying to stab an FBI surveillance officer.

The FBI accused Saleh of trying to recruit Topaz, who was allegedly making plans to travel to join ISIL in the Middle East.

The pair allegedly met up at a Manhattan subway station a few blocks from the World Trade Center on May 31.

Prosecutors in New York have also accused Saleh of planning to carry out a bomb attack in the city.

Topaz allegedly posted selfies on Facebook dressed in militant-style head garb and wrote about his intention to go to Jordan, which prosecutors called a cover story for travel to ISIL-controlled territory.

Court papers released on Thursday listed two other co-conspirators, both of whom were dual US-Jordanian citizens.

After his arrest, prosecutors said Topaz confessed to sympathizing with ISIL cause.

Prosecutors in Boston announced later Thursday that Massachusetts man David Wright, 25, and Rhode Island resident Nicholas Rovinski, 24, were also indicted with conspiracy to provide material support to ISIL.

Wright was also charged with conspiracy to obstruct and with obstructing justice. They are due to appear in court on Friday.

US intelligence officials warned in February that more than 20,000 volunteers from around the world, including more than 150 Americans, had gone to Syria to link up with extremists.