Two New York Muslims were hauled before a federal court Wednesday charged with plotting to join Islamic State extremists in Syria and threatening to carry out attacks in the United States.

FBI agents arrested Akhror Saidakhmetov, 19, at John F. Kennedy airport allegedly attempting to board a flight to Istanbul and Abdurasul Hasanovich Juraboev, 24 -- who had offered to kill President Barack Obama -- was detained at home in Brooklyn.

A third New York resident, Abror Habibov, 30, was arrested in Jacksonville, Florida accused of funding Saidakhmetov's jihadist quest.

The arrests come with Western governments increasingly concerned about a rising number of foreign fighters travelling to Syria through Turkey to join extremist groups.

Saidakhmetov is Kazakh while the other two come from Uzbekistan. It was not clear how long they had been in the United States.

Last month, a spokesman for the Islamic State (IS) group issued a call on Muslims in the West to carry out new attacks and the extremist network is thought to prey on vulnerable young people through social media.

"The flow of foreign fighters to Syria represents an evolving threat to our country and to our allies," said Loretta Lynch, Attorney General nominee and US attorney for the eastern district of New York.

"Anyone who threatens our citizens and our allies, here or abroad, will face the full force of American justice."

US prosecutors said Saidakhmetov wanted to buy a machine gun and shoot US police officers and FBI agents if blocked from fighting in Syria.

Prosecutors said Juraboev posted a message online last August offering to kill Obama if ordered to do so by IS, which has overrun large swathes of Iraq and Syria.

They said Juraboev bought a plane ticket to travel to Istanbul next month, also planning to make his way to Syria and wage war on behalf of IS.

The three men have been charged with attempt and conspiracy to provide material support to a foreign terrorist organization.

If convicted they face a maximum sentence of 15 years in prison.

- Gasps in court -

Juraboev and Saidakhmetov attended a 10-minute hearing before Magistrate Judge Lois Bloom at the federal court house in Brooklyn, but have yet to be indicted and entered no plea.

Dressed in jeans, rolled up at the ankle, sneakers and hoodies, they stood with their hands behind their backs. Speaking through an interpreter they said they understood their rights.

There were gasps in court at Saidakhmetov's youthful appearance -- his lawyer said he had not completed high school -- while Juraboev sported wispy facial hair and wore a Muslim-style prayer cap.

Prosecutor Doug Pravda said both men posed a "significant threat" to the community and a "substantial" flight risk if released on bail.

Bloom ordered them detained until further notice and set a preliminary hearing for March 11.

Saidakhmetov's court-appointed lawyer, Adam Perlmutter, said his client was innocent until proven otherwise and criticized the government's approach to Muslim men.

"They are very ham-fisted tactics. There were no attempts to intervene to speak to explore, to understand. There is just the rush to prosecution, to arrest and to conviction," he told reporters.

- Foreign fighter task force -

FBI Director James Comey said Wednesday that suspected IS supporters are under investigation in all 50 states across the United States and that the terror group deploys "slick propaganda through social media."

He told the National Association of Attorneys General that the invitation to join them or kill people where they are "resonates with troubled souls, people seeking meaning in some horribly misguided way."

In Washington, Republican and Democrat representatives announced the creation of a task force to assess the government's efforts to obstruct foreign fighter travel and prevent terror attacks at home.

Attacks in Paris against a magazine and kosher supermarket killed 17 people in January, after which IS spokesman Abu Mohamed al-Adnani called on Muslims in the West to carry out fresh assaults.

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

Nicholas Rasmussen, director of the National Counter-Terrorism Center, said the rate of travel to Syria was "unprecedented" and exceeds the number who went anywhere else, such as Afghanistan or Pakistan, in the last 20 years.