Syria has detained the prominent writer and democracy campaigner Michel Kilo.
Family and a local rights organisation say Kilo, 66, was detained on Sunday, days after he signed a petition calling for steps to improve Lebanese-Syrian relations.
Kilo's daughter, Shaza, said her father was summoned by the security police at noon on Sunday and did not return home.
The government did not confirm his arrest, but the authorities almost never issue statements about detentions that are deemed a security matter.
Kilo has long been an critic of the Syrian government, which tightly controls national politics and often arrests its critics.
He has called for reform in Syria and has criticised the government's involvement in the political affairs of its smaller neighbour, Lebanon.
He is a political analyst and a well-known writer whose works are frequently published by Lebanese newspapers, including the leading anti-Syrian paper Al-Nahar.
Ammar Qurabi, the head of the National Organisation for Human Rights, said he had no information on the reason for Kilo's arrest, but said it might be connected to Kilo's signing of the petition calling for better relations with Lebanon.
About 500 Syrian and Lebanese intellectuals signed the document last week.
Relations between Lebanon and Syria plummeted after the assassination last year of Rafiq al-Hariri, the former Lebanese prime minister. Many Lebanese blamed the death on Syria.
A UN-mandated investigation has implicated officials of the Syrian intelligence service, but Damascus has denied any involvement.
Syria has recently stepped up its arrest of human rights activists and critics.
Amnesty International, the human rights watchdog based in London, criticised the government last month for the detentions, describing them as another blot on the country's poor human rights record.