LJUBLJANA, Slovenia (AP) — Slovenia's prime minister says he is resigning after the country's top court annulled last year's referendum on a key railway project and ordered a new vote.

Miro Cerar says that he has sent his resignation to parliament.

Slovenia's Supreme Court ruled earlier Wednesday that government backing for the project during the referendum campaign was one-sided and could have affected the outcome of the vote.

The referendum last September approved the government's plan to build 27 kilometers (16 miles) of additional railway linking the Adriatic port of Koper with the Divaca hub near the border with Italy.

The vote was initiated by independent campaigner Vili Kovacic who also took the issue to Slovenia's top courts.