Human Rights Watch (HRW) on Wednesday accused the Jordanian authorities of forcibly returning some Palestinians from Syria and threatening others with deportation.

"Since April 2012, the authorities have also arbitrarily detained Palestinians fleeing Syria in a refugee holding centre without any options for release other than return to Syria," the US-based watchdog said in a statement.

"The Jordanian authorities should treat all Palestinians from Syria seeking refuge in Jordan the same as Syrian asylum seekers, who are allowed to remain and can move freely in Jordan after passing security screening and finding a sponsor."

The United Nations said in May that around 500 Palestinian refugees have fled Syria to Jordan since the revolt against President Bashar al-Assad's regime began last year.

HRW said it has interviewed dozens of those refugees.

"To its credit, Jordan has allowed tens of thousands of Syrians to cross its borders irregularly and move freely in Jordan, but it treats Palestinians fleeing the same way differently," said Gerry Simpson, senior refugee researcher and advocate for HRW.

Jordan, home to more than two million Palestinian refugees, is hosting around 140,000 Syrians, and 27,344 of them are UN-registered.

"All those fleeing Syria -- Syrians and Palestinians alike -- have a right to seek asylum in Jordan, move freely in Jordan, and shouldn't be forced back into a war zone," Simpson said.

HRW said Jordanian officials have denied these accusations, but "Palestinians contradicted these assertions."

The rights group said Jordan "should extend its current policy of providing de facto temporary protection to Syrian 'guests' to include Palestinian residents of Syria who are also fleeing the conflict there."

"There can be no excuse for deporting people to a situation where there is a real risk to their lives," Simpson said.

More than 16,500 people have been killed in violence in Syria since the mid-March last year, according to the Syrian Observatory for Human Rights.