* Australian police disrupt "Islamic-inspired" plot to down plane
* Abu Dhabi's Etihad says helping with Australian investigation
* Stricter security screening imposed at airports across Australia
* Security service interruption communications with Islamic State
* Sydney homes raided, four men held under special security powers (Recasts throughout with Etihad statement and details of investigation)
By Jamie Freed and Alexander Cornwell
SINGAPORE/DUBAI, Aug 1 (Reuters) - Abu Dhabi's Etihad Airways said on Tuesday it was helping Australian Federal Police with an investigation that police began into an "Islamic-inspired" plot to bring down a plane and resulted in stricter security screening at Australian airports.
Four men were arrested in raids in several suburbs in Sydney, Australia's largest city, at the weekend and are being held without charge under special terror-related powers.
"The Etihad Airways aviation security team is assisting the Australian Federal Police with its investigation and the matter is ongoing," Etihad said in a statement.
"Etihad is complying fully with the enhanced security measures at airports in Australia and monitoring the situation closely," it said.
Police have not identified the airline that was allegedly targeted in the plot, nor the specific means that were to be used to bring it down, other than to say it involved an "improvised device".
U.S. officials, who spoke to Reuters on condition of anonymity, said a foreign intelligence service had intercepted communications between the plotters in Sydney and members of the Islamic State militant group in Syria. The officials declined to identify the foreign intelligence service. two U.S. officials familiar with the Australian arrests said a developing plot had been detected. One of them, also speaking on condition of anonymity, said the alleged plot was "fairly well along" when it was disrupted by Australian authorities.
The other official said the target appeared to have been a commercial flight from Sydney to the Gulf.
The arrests have disrupted air travel in Australia, where authorities and airlines have asked travellers to arrive earlier than usual for additional screening.
The houses of the detained men were still being searched on Monday evening, two days after the arrests. A single black police four-wheel-drive vehicle was parked at one of the raided homes in the inner Sydney suburb of Surry Hills.
Forensics officers had also set up a tent for objects taken from the house, according to a Reuters witness. A police officer at the scene declined to comment.