(Adds police commissioner citing "Islamic-inspired terrorism" for raids, byline, background, quotes)
By Benjamin Cooper
SYDNEY, July 30 (Reuters) - Security has been increased at Australian airports after police foiled "Islamic-inspired" plans for a bomb attack on an aircraft during counter-terrorism raids in which four men were arrested on Saturday, the Australian Federal Police (AFP) have confirmed.
"In recent days, law enforcement has become aware of information that suggested some people in Sydney were planning to commit a terrorist act using an improvised device," AFP commissioner Andrew Colvin said during a press conference with Prime Minister Malcolm Turnbull on Sunday, adding:
"We do believe it is Islamic-inspired terrorism. Exactly what is behind this is something that we will need to investigate fully.
"At this time we don't have a great deal of information on the specific attack, the location, date or time. However, we are investigating information indicating that the aviation industry was potentially a target ..."
Five properties were searched on Saturday across the Sydney suburbs of Surry Hills, Lakemba, Punchbowl and Wiley Park. The commissioner said four of those searches may continue for days.
An AFP spokesman told Reuters the men had not been charged as of Sunday morning.
Turnbull said advice from Australian security and intelligence agencies had led to increased security measures at Sydney airport on Thursday, while the country's other domestic and international airports were affected from Saturday.
"Some of the measures will be obvious to the public, some will not be," Turnbull said.
Colvin said travellers could expect an increased police and security agency presence at airports.
"You can expect longer delays to make sure that more screening is being done on baggage, both hold luggage as well as hand luggage," adding that travelers should allow more time to get through security.
Australia, a close ally of the United States, has been on heightened alert for attacks by home-grown militants returning from fighting in the Middle East, or their supporters, since 2014.
Authorities say they have thwarted a number of potential attacks since then but there have been several "lone wolf" assaults, including a cafe siege in Sydney that left two hostages and the gunman dead.
About 100 people have left Australia for Syria to fight alongside organizations such as Islamic State, Australia's immigration minister said last month.