The European Union expressed concern on Monday about a second visit to Chad by Sudanese President Omar al-Bashir, saying he should have been arrested there under an International Criminal Court warrant.

An EU statement welcomed the improvement and normalisation of the relations between Chad and Sudan, but noted Chad was a signatory to the ICC statute and stressed the importance of implementing U.N. resolutions.

EU foreign policy chief Catherine Ashton expressed concern about Bashir's Sunday visit and urged Chad "to respect its obligations under international law to arrest and surrender those indicted by the ICC," the statement said.

"Crimes against humanity and war crimes must not go unpunished and their prosecution must be ensured by measures at both domestic and international level," it said.

The ICC issued an arrest warrant last year for Bashir for orchestrating genocide in the Darfur region, where as many as 300,000 people have died since 2003.

This followed an earlier warrant issued in March 2009 for war crimes and crimes against humanity. Bashir has dismissed the charges by the ICC, the world's first permanent court for prosecuting war crimes, as part of a Western conspiracy.

The ICC warrants were the first issued against a sitting head of state by the court, but Bashir remains at large as the ICC has no police force and depends on national authorities and states that have signed up to the court to make arrests.