The United Nations has called on Bahrain to release a human rights activist detained for sending a tweet that offended the country's Interior Ministry.

A spokesman for the Geneva-based U.N. human rights office says the detention of Nabeel Rajab sends a "chilling message" to others in the Persian Gulf nation that they too could face reprisals if they speak out.

Rupert Colville said Friday that Rajab was detained Wednesday upon his return from an overseas trip that included a meeting with U.N. human rights officials in Geneva to discuss the situation in Bahrain.

Colville welcomed the Oct. 1 release and lifting of a travel ban on another prominent Bahraini activist, Maryam al-Khawaja. Her trial for allegedly assaulting two police officers has been set for Nov. 5.