More than 100 Syrian refugees have been forcibly returned to their conflict-ridden country by Lebanese authorities after arriving at Beirut's airport en route to Turkey, Amnesty International said on Friday.

Another 150 Syrians are also at risk of imminent deportation.

Sherif Elsayed-Ali, head of refugee and migrants' rights at Amnesty, slammed the move to send them to Damascus in statement, saying "Lebanese authorities stooped to a shocking new low" while "putting these people in mortal danger".

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"This is an outrageous breach of Lebanon's international obligations to protect all refugees fleeing bloodshed and persecution in Syria. The Lebanese government must halt all further deportations of refugees from Syria immediately," he said.

The UK-based rights group also said Lebanese authorities are planning to send back another 150 refugees, who have been stranded at Rafik Hariri International Airport because of new Turkish entry restrictions imposed on Friday.

"They were due to depart on Thursday but were unable to leave," Elsayed-Ali said.

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According to the Reuters news agency, an airport official said about 400 Syrians transiting through Beirut were prohibited from boarding flights to Turkey with its new restrictions, part of efforts to stem the flow of refugees into Europe.

Elsayed-Ali added: "The new visa regulations in Turkey present yet another hurdle for Syrians desperate to seek sanctuary from the conflict, and show what devastating consequences such restrictions can have for refugees."

Turkey is home to more than 2.2 million Syrians, the world's largest refugee population.