Police in the Caribbean state of Trinidad are searching for a fourth man charged with plotting to blow up New York's John F Kennedy Airport.
The man, Abdel Nur, is believed to be at large on the island.
Three other suspects are in custody, accused of conspiring to blow up fuel tanks and pipelines serving the airport, one of the world's busiest.
The suspects include a former cargo worker and an ex-MP for the South American nation of Guyana.
The plot - which is said not to have gone past the planning stages - involved blowing up the airport's fuel tanks and pipeline, US justice department officials said.
One of the arrests was made in New York and the other two took place in Trinidad.
Guyanese citizen Abdul Kadir, a former member of Guyana's parliament, and Kareem Ibrahim, from Trinidad, are in custody in Trinidad and Tobago.
The authorities said both men were associates of Jamaat al Muslimeen, a Muslim organisation behind a coup attempt in Trinidad in 1990.
The former JFK cargo worker was arrested in Brooklyn late on Friday and named as Russell Defreitas, originally from Guyana.
Mr Defreitas was arraigned in New York City on Saturday afternoon, but did not enter a plea.
JAMAAT AL MUSLIMEEN
Muslim social group in Trinidad
140 members took part in 1990 coup attempt
Stormed parliament and Trinidad and Tobago TV, taking cabinet hostage
24 people died during coup
Coup led by Yasin Abu Bakr, former Trinidadian policeman
Those jailed for the coup were freed in 1992
Accused of links to criminal gangs
He is to be held pending a bail hearing on Wednesday, US prosecutors said.
It was "one of the most chilling plots imaginable," US attorney Roslynn Mauskopf told a news conference.
"Had the plot been carried out, it could have resulted in unfathomable damage, deaths and destruction."
The pipeline is 40 miles (64km) long and carries jet fuel from New Jersey and through the New York boroughs of Staten Island, Brooklyn and Queens.
The pipeline serves two other airports in the area - LaGuardia and Newark Liberty.
The FBI said the alleged plot never got beyond the planning stages and there was no threat to air safety or to the public, but that the group's intentions were never in doubt.
"One clear signature of this cell was its persistence, they consistently worked to refine their plot," said Mark Mershon of the FBI's New York office.
"They took extensive measures to seek expert advice, finances and explosives."
The alleged plot was brought to light when Mr Defreitas recruited an FBI informant to help him in the plan, officials said.
Mr Kadir is one of the three men already arrested
The men conducted surveillance of the airport, including videotaping their targets and downloading satellite images from the internet, officials said.
They said the informant had recorded some of the conversations he had with Mr Defreitas.
"Any time you hit Kennedy, it is the most hurtful thing to the United States," Mr Defreitas said, according to a recording played to reporters.
"To hit John F Kennedy, wow... they love John F Kennedy like he's the man... if you hit that, this whole country will be in mourning. You can kill the man twice."
In another recorded conversation the suspect was alleged to have said: "Even the twin towers can't touch it," referring to the attack on the World Trade Centre in New York City on 11 September 2001 that killed some 3,000 people.
"This can destroy the economy of America for some time," Mr Defreitas was alleged to have said.
Mr Kadir studied at the University of Guyana and at the Trinidad campus of the University of West Indies, the Associated Press (AP) reported.
Mr Kadir's wife said her husband knew Mr Nur in the 1980s, but the pair were no longer in contact, AP reported.
"We have not seen him for a long time and I would be surprised if my husband has any links with him still," the agency quoted her as saying.
The arrests are the latest in a series of alleged plots targeting American facilities and landmarks.
Six men were arrested last month on charges of plotting to attack Fort Dix army base in the state of New Jersey.
Three people were arrested in July last year outside the US in connection with a plan to suicide bomb the tunnel under the Hudson River connecting Manhattan with New Jersey.
And in June 2006, seven suspects were charged over an alleged plot to destroy the country's tallest building - the Sears Tower in Chicago.