Italian giant Eni and fellow petroleum company Shell will stand trial in Italy over allegations of bribery and corruption in the 2011 purchase of an offshore oil block in Nigeria.

A judge in Milan ordered Eni, Shell and key figures such as Eni chief Claudio Descalzi and his predecessor Paolo Scaroni to stand trial in proceedings to begin March 5.

The companies are accused of corruption in the 2011 purchase of OPL245, an offshore oil block estimated to hold 9 billion barrels of crude, for $1.3 billion.

"Eni's Board of Directors has reaffirmed its confidence that the company was not involved in alleged corrupt activities in relation to the transaction," the Italian firm said in a statement Wednesday.