Portuguese Prime Minister António Costa abruptly resigned on Tuesday, hours after police raided his residence, government ministries and other properties as part of a major corruption probe.
Costa said in a brief televised address that he had handed in his resignation to President Marcelo Rebelo de Sousa.
"As I understand it, the position of prime minister is not compatible with any suspicion about his integrity or good conduct and certainly not with any suspicion of having committed a criminal act," he said.
The Socialist politician said he had a "clear conscience" and had been "surprised" by the investigation.
The probe revolves around suspicions of bribery and favouritism in the allocation of concessions for lithium mining in the Montalegre area and the production of green hydrogen near the southern town of Sines, the state news agency Lusa, the state broadcaster RTP and other Portuguese media reported.
Five people were reportedly detained, including Costa's Cabinet chief Vítor Escaría. Entrepreneur Diogo Lacerda and the mayor of Sines, Nuno Mascarenhas, as well as two other businessmen, were also taken into custody, RTP and Lusa said.
It was not initially known what exactly each was accused of.
The prosecutor's office confirmed that searches had been conducted at dozens of residences and offices, including the ministries of Infrastructure and Environment, as well as Costa's residence.
But neither prosecutors nor police have provided further details.
The region of Montalegre in the far north of Portugal is believed to have the largest lithium deposits in Europe, which are set to be mined despite strong opposition from residents. The metal is crucial for battery production.
A decommissioned coal-fired power facility in Sines, near the capital Lisbon, ceased operations in 2021, but it is now positioned to produce green hydrogen by harnessing sustainable energy sources.
Both projects are seen as essential components of Portugal's transition away from the use of fossil fuels.
The shock resignation came after opposition parties demanded Costa, 62, step down and new elections be held. He has been prime minister since 2015.
Rebelo de Sousa can now appoint an interim head of government and dissolve parliament. There will then have to be a new election.
Until Tuesday morning, Costa was considered the favourite in the next regular parliamentary election, which was not expected until 2026, according to polls.
Costa's resignation brings an almost eight-year success story to a sudden halt.
It was only in January 2022 that Costa and his Socialist Party (PS) won an absolute majority in Lisbon's national parliament, the Assembleia da República. Prior to that, he had confidently led left-wing minority governments since the end of 2015.
After the difficult years of the euro crisis, Costa was credited for the much-celebrated Portuguese economic "miracle." Since 2016, economic growth in the small country with a population of just 10.3 million has almost always been above the EU average.
The unemployment rate has fallen rapidly and recently stood at just over 6%. Costa's government in October hiked the monthly minimum wage from €505 ($540) to €820.
