Four Muslims were arrested in New York as they allegedly planted what they thought were car bombs outside two synagogues in the Bronx.

The home-grown terror plot was thwarted by an elaborate FBI sting operation that supplied the would-be terrorists with fake plastic explosives and a deactivated Stinger anti-aircraft missile.

The four suspects, described as “petty criminals” who met in jail, were charged with plotting to blow up the synagogues and shoot down a military aircraft at an airport in upstate New York.

Police tracked their plans for a year through an informer and pounced as they place the dud bombs outside the synagogues in the Riverdale section of the Bronx.

“No one was at risk. This was a tightly controlled operation. But these individuals did in fact place these bombs — or what they thought to be bombs — in front of buildings,” Ray Kelly, the New York police commissioner, said.

“They stated that they wanted to commit jihad. They were disturbed about what was happening in Afghanistan and Pakistan, that Muslims would be killed. They made the statement that if Jews were killed in this attack, that would be all right.”

Officials said that the men fell foul of “trip wires” the FBI had set up by recruiting informers at mosques and other key locations after the al-Qaeda attacks on America in 2001.

Three of the suspects were American citizens — including one of Afghan descent — and the fourth was a Haitian immigrant. Some of them converted to Islam in prison. All used Arabic aliases.

The alleged ringleader is James Cromitie, 53, or “Abdul Rahman,” the son of an Afghan immigrant father and an African-American mother.

A shelf-stacker at a Wal-Mart supermarket, Mr Cromitie has a criminal record of 27 previous arrests and has been to jail three times on drug charges.

The other alleged conspirators were David Williams, known as “Daoud”; Onta Williams, or “Hamza”, who served a year in prison for attempted assault; and Laguerre Payen, a Haitian who uses the name “Amin” and served three months in prison on drug charges.

All four live in Newburgh, about 70 miles north of New York City.

According to court papers, Mr Cromitie was angry at the US war in Afghanistan, where his parents lived before he was born. He allegedly said he wanted to do “something to America” but complained that “the best target [the World Trade Centre] was already hit”.

Prosecutors say that Mr Cromitie approached a man at a Newburgh mosque whom he believed to be connected to the outlawed Pakistani terror group Jaish-e-Mohammed.

The man was an informer who had been co-operating with the FBI since being sentenced to five years’ probation for fraud in 2002.

At a meeting in April 2008, Mr Cromitie allegedly told the informer of his plans to bomb synagogues and shoot down military aircraft at the Air National Guard base at Stewart airport in Newburgh.

The informer procured a deactivated Stinger missile and sold the alleged plotters a cache of military-grade C4 explosives that had been doctored by FBI experts to render them inert.

Police reportedly watched the group on a live video stream as they planted what they thought were explosives at around 9pm local time on Wednesday.

Mr Cromitie, with the informant acting as his driver, allegedly placed a satchel containing the dud explosive in a Pontiac car outside the Riverdale Temple on Independence Avenue and then placed more inert explosives in a 4x4 vehicle outside the Riverdale Jewish Centre.

As they tried to leave police blocked their 4x4, broke a tinted back window to see inside and arrested them.

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