Portuguese Prime Minister Antonio Costa announced his resignation on Tuesday after he was embroiled in a corruption investigation into the awarding of energy-related contracts.

“The duties of prime minister are not compatible with any suspicion of my integrity,” Costa told a press conference after briefly speaking with President Marcelo Rebelo de Sousa earlier on Tuesday.

“In these circumstances, I have presented my resignation to the president of the Republic,” he added.

Earlier Tuesday, Portuguese media reported that investigators had searched several ministries as well as Costa’s offices.

Public prosecutors later said they had indicted Infrastructure Minister Joao Galamba and issued an arrest warrant for Costa’s chief of staff.

The investigation covers alleged “misuse of funds, active and passive corruption by political figures, and influence peddling,” according to a statement from public prosecutors.

A separate probe is looking into Costa, who is alleged to have intervened personally to speed up the contracts, the statement said.

The investigation covers lithium mining concessions in the north of the country, as well as a hydrogen production project and data centre to be built by the company Start Campus in Sines, a town about 100 kilometres (62 miles) south of Lisbon.

Citing flight risk and the possibility that illegal activity could continue, arrest warrants were also issued for the mayor of Sines and two executives at Start Campus.

The president of the executive board of the Portuguese Agency for the Protection of the Environment (APA) was also indicted.

APA in May approved a lithium mining project, an essential metal for the manufacturing of electric batteries.

A second project was given the green light at the start of September. The projects are opposed by environmental groups and part of the local population.

Portugal has the largest lithium reserves in Europe and is the continent’s leading producer, but its current output goes entirely to the ceramic and glass-making industries.

ACosta, from Portugal’s Socialist Party, has been prime minister since late 2015 and was reelected in January 2022. His popularity has recently declined after a series of scandals linked to the national airline TAP.