Police in Florida have released three men detained on Friday after a potential terror alert turned out to be a false alarm.

If this was a hoax, they will be charged

Sheriff Don Hunter

The authorities held the three for 17 hours, shut down a major highway, and searched their cars for explosives - but found nothing threatening.

Police took action after a customer in a restaurant alleged she overheard the men - said to be of Middle Eastern appearance - discussing plans for an attack.

But the three were shown to be medical students attending a conference.

They are of Jordanian, Iranian, and Pakistani descent - one is a US native, another a naturalised citizen, while the third holds a valid visa, the authorities say.

'Spicing up the story'?

Eunice Stone, a 44-year-old nurse from Cartersville, Georgia, told police she heard a conversation in which one of the three said Americans had mourned on 11 September and would mourn again on 13 September.

Ms Stone is accued of "adding salt and pepper" to her report

The Georgia Bureau of Investigation asked other police forces to watch out for the vehicles after the waitress gave a description, including license-plate details.

The cars were pulled over after a sheriff's deputy spotted them in southern Florida.

"If this was a hoax, they will be charged," Collier County Sheriff Don Hunter said.

But after their release, the students denied that making any comments or jokes about terrorism.

One the three - Ayman Gheith, who has a long beard and wore a skull cap at the rest stop - said the waitress may have been influenced by his appearance.

"She saw obviously the way I was dressed and maybe she put a little salt and pepper into her story," he said.

Controlled explosion

Mr Gheith, Omer Choudhary and Kambiz Butt were tracked and spotted early on Friday, after one of their two vehicles reportedly passed through a road toll booth without paying.

The cars were searched for several hours

Sniffer dogs and a robot were used to search the vehicles for explosives, and live television showed a bomb squad team blowing up what appeared to be a backpack.

Police shut Alligator Alley - the main east-west route across the Florida Everglades - for several hours.

The US has been on heightened alert against terror threats for the first anniversary of the 11 September attacks.

The BBC's Justin Webb in Washington says there have been a number of similar incidents in recent days, but so far they have all turned out to be innocent misunderstandings or mistakes.