The Office of the Attorney General of Switzerland (OAG) has blocked various bank accounts in Switzerland regarding an alleged oil bribery scheme linked to Nigeria. Executives from oil giants Shell and Eni are due to stand trial in Milan, Italy, in May.

At the request of the Milan public prosecutor, the Swiss authorities have confiscated assets and provided information and assistance to the Italian authorities, the Swiss attorney general’s office confirmed on Monday.

The new move has sent jitters among Nigeria’s political elite some of whom were said to have eaten the forbidden fruit as they got chunks in what has been described as the biggest corporate bribery in the world.

Information gleaned by Political Economist from Swissinfo.ch said the British oil giant Shell and its Italian counterpart Eni were due to stand trial on Monday in the Italian city of Milan in what in Nigeria has been dubbed the Malabu oil deal. However, the trial was postponed until May 14, Reuters reported on Monday. Nigerian and Italian courts accuse officials from both companies of having paid bribes to secure a licence for an oil field off the Africa country. The case has been billed as one of the biggest ever corruption cases in Europe by anti-corruption campaigners.

The exploration permit, which concerns an oil block called OPL-245 in the Gulf of Guinea off Nigeria, was issued in 2011 by the Nigerian government to the two companies for $1.3 billion (CHF1.2 billion).

Three separate bank accounts in Lugano, Basel and Geneva were blocked, according to a report in German-speaking Tages-Anzeiger newspaper on Monday. The prosecution confirmed this, but declined to comment on the value of the assets which were seized. The Tages-Anzeiger cited “several hundred million francs”, while the Nigerian authorities quoted a bribery sum of $801 million.

In all, 13 people have been accused, including Eni boss Claudio Descalzi, and his predecessor Paolo Scaroni, two former top Shell managers, former Nigerian oil minister, Dan Etete and a series of middlemen and advisers. The companies themselves are also corporate defendants. Both oil companies have denied wrongdoing and expressed confidence that the trial would exonerate both the companies and individuals.