The office of the International Criminal Court prosecutor expressed concern Thursday about post-election violence in Nigeria and said it would investigate whether crimes had been committed.

"The office of the prosecutor is closely following on the situation in Nigeria and is concerned with the outbreak of violence surrounding the National Assembly and presidential elections of April 2011," a statement said.

"The office will seek to establish whether the recent violence may have been planned and organized and whether crimes falling within the court's jurisdiction may have been committed."

The ICC, based in The Hague, is the world's only independent, permanent tribunal with the jurisdiction to try genocide, crimes against humanity and war crimes.

It can only pursue charges if a member state is unwilling or unable to do so.

Prosecutor Luis Moreno-Ocampo's office said it was mindful that governorship elections on April 26 could lead to further violence, and warned that "those who commit atrocities to gain power will be held to account".

Curfews and military patrols have largely restored calm after rioting broke out in northern Nigeria following southern incumbent Goodluck Jonathan's election win over northerner Muhammadu Buhari at the weekend and quickly spread across the region.

A Nigerian rights group says more than 200 people were killed, but authorities have refused to provide a death toll, fearing it could provoke reprisals. The number of displaced has risen to 60,000, the Red Cross says.

The office of the prosecutor opened a preliminary investigation in 2004 into alleged crimes committed in central Nigeria, which signed up to the court's founding Rome Statute in 2001.