BEIRUT — Lebanese authorities have detained a Palestinian human rights activist after he was summoned to a security agency in Beirut, an international rights group said Tuesday.

Human Rights Watch said Ghassan Abdallah, director of the Palestinian Human Rights Organization, or PHRO, was detained after being summoned to the General Security Directorate early Monday and was held incommunicado for more than 24 hours.

It quoted his lawyer as saying that Abdallah has since been transferred to Military Intelligence. It said Abdallah was able to make a telephone call and has access to medication. Authorities have not clarified the basis of his detention or allowed him to speak with his lawyer, Human Rights Watch said.

Lebanese officials could not immediately be reached for comment.

PHRO said no reason was given by authorities for Abdallah's detention, adding that since he was summoned he only called his mother. It added that Abdallah holds Lebanese and Canadian citizenship, and is one of its founding members.

The organization campaigns for the rights of Palestinians living in Lebanon and documents violations.

About 175,000 Palestinian refugees and their descendants live in Lebanon, most of them in the country's 12 refugee camps. The refugees fled or were expelled from what is now Israel during the 1948 war around its creation.

Palestinians in Lebanon held demonstrations Tuesday to mark the 70th anniversary of the "nakba," or catastrophe, their term for the mass uprooting.

The influx of the Palestinians upset Lebanon's fragile sectarian balance, and Palestinian militancy was a key factor behind the 1975-1990 civil war. Palestinians do not have Lebanese citizenship and face restrictions in owning property and in employment, including in the banking sector.

It was not immediately clear if Abdallah's detention was linked to the Palestinians' mass protests in Gaza.