Italy's embassy in Libya and those of Austria, Belgium, Bulgaria, Finland, France, Germany, the Netherlands, Portugal, Spain, Sweden and Britain, have urged the "immediate" release of Siham Sergiwa, a politician and prominent rights activist who was abducted in Benghazi in July.
The embassies and the European Union delegation "express their deep concern" for Sergiwa "and call for her immediate release," said the statement tweeted by the Italian embassy in Libya on Monday.
"We continue to call on relevant Libyan authorities to conduct urgent investigations into her disappearance, and provide an update on her whereabouts," said the joint statement issued on Sunday.
Sergiwa, 56, vanished on 17 July after an attack on her home by an armed group in Benghazi, which is controlled by militias loyal to eastern warlord Khalifa Haftar.
A member of the Tobruk-based House of Representatives, Sergiwa may have been kidnapped by Haftar's forces after she made critical remarks in an interview with a pro-Haftar TV channel Al Hadath, according to her relatives.
"The trend of attacks against politicians, political activists and members of civil society, and in particular women, is unacceptable," said the statement.
The signatories also warned that violations of international humanitarian and human rights laws in Libya will not go unnoticed and perpetrators "will be held accountable".
The United Nations has also urged a probe into Sergiwa's disappearance and appealed to her captors to free her immediately.