Urgent efforts are under way to establish the whereabouts of the Guardian correspondent Ghaith Abdul-Ahad, who has been reporting from western Libya for the past two weeks.

Abdul-Ahad entered the country from Tunisia and was last in touch with the paper through a third party on Sunday, when he was on the outskirts of Zawiya, a town west of the capital, Tripoli, which has seen fierce fighting in the past few days.

The Guardian has been in contact with Libyan government officials in Tripoli and London and asked them to urgently give all assistance in the search for Abdul-Ahad and to establish if he is in the custody of the authorities.

Abdul-Ahad, who is an Iraqi national, is a highly respected staff correspondent who has written for the Guardian since 2004. He has spent long periods in Somalia, Sudan, Iraq and Afghanistan, reporting on the stories of ordinary people and their suffering in times of conflict.

He has won many of the most prestigious awards available to foreign correspondents, including foreign reporter of the year at the British Press Awards, the James Cameron award and the Martha Gellhorn prize. He was shortlisted in February in the foreign reporter of the year category at this year's UK Press Awards.

Abdul-Ahad was travelling with Andrei Netto of the Brazilian newspaper Estado. Netto is also missing.