The Maltese prime minister’s chief of staff and the country’s tourism minister have resigned in an escalation of the political turmoil surrounding the investigation into the murder of the prominent anti-corruption journalist Daphne Caruana Galizia in 2017.

“Yesterday evening, my chief of staff informed me that from today he would be relinquishing his post,” the prime minister, Joseph Muscat, said at a brief press conference on the steps of his office on Tuesday morning.

Keith Schembri is understood to have been taken to police headquarters for questioning in relation to the case, and police were seen entering one of his properties on Tuesday. Schembri made no immediate comment.

Later on Tuesday, the tourism minister, Konrad Mizzi, announced his resignation after a cabinet meeting. Mizzi said he resigned “in light of political, extraordinary and general circumstances in the country”.

“I have done nothing wrong from a criminal point of view,” he added.

Schembri and Mizzi had both been accused of corruption by Caruana Galizia. They have always denied any wrongdoing.

Schembri’s resignation followed reports on Monday night that a businessman arrested last week in connection with the murder was preparing to make allegations against Schembri.

Opposition politicians have been calling for both men to go since Caruana Galizia reported that they had taken control of secretive Panama shell companies soon after entering office.

Asked whether he would consider his own position, Muscat said: “I have always said I don’t intend seeking re-election. I don’t intend to serve more than two terms. My role right now is to make sure that we navigate through this turbulent time in the best possible manner. Once this chapter is closed with the arraignment of person or persons on this case I will make my consideration.”

Muscat added: “I would definitely resign if there is any sort of association between myself and the murder.”

Chris Cardona, the minister for the economy, investment and small businesses, also said that he was “suspending himself with immediate effect … pending the investigations and proceedings going on right now”. Cardona said he had absolutely no connection with the Caruana Galizia case, but after police had asked for further clarifications, he felt duty bound to take the step in the national interest.

Quick guide Daphne Caruana Galizia investigation: who's who Show Hide Daphne Caruana Galizia Malta's best-known investigative journalist was killed in a car bomb as she left her home in October 2017. Alfred Degiorgio, George Degiorgio and Vincent Muscat Three men in their fifties arrested in December 2017 and then formally charged in July 2019 with Caruana Galizia’s murder, criminal conspiracy and the criminal use of explosives. Melvin Theuma A taxi driver from Birkirkara and suspected middleman in the Caruana Galizia case, he was arrested on 14 November 2019 in a separate money laundering case. He has offered to provide information he says he has on the journalist's death in exchange for a pardon. Yorgen Fenech A prominent businessman arrested onboard his yacht as a person of interest in the Caruana Galizia investigation on 20 November 2019. One of the journalist's final investigations was a leak of data from his businesses. He has previously denied any wrongdoing. On 28 November his lawyers deposited a letter in court to Malta’s president formally asking for a pardon in return for information relating to the case. On 29 November the request was turned down. Keith Schembri and Konrad Mizzi The Maltese PM's chief of staff and the tourism minister resigned on 25 and 26 November 2019 respectively. Caruana Galizia reported that they had taken control of secretive Panama shell companies soon after entering office. They deny any wrongdoing. Schembri was arrested on 26 November and released on 28 November. Police said that after an 'intensive investigation' they no longer felt the need to hold him. Joseph Muscat Malta’s prime minister who served between 2013 to 2020. He was criticised by opposition politicians for allowing Schembri and Mizzi to stay in their posts. Having said on 29 November 2019 that he would stay in the job until the investigation into the murder was complete, on 1 December in a televised address he instead announced that he would stay on until a new leader of his ruling Labour party was elected in January. The prime minister expressed “deep regret” for Caruana Galizia’s murder and spoke of the need for a “fresh page”. Photograph: Darrin Zammit Lupi/X01097

Manfred Weber, the head of the centre-right EPP grouping in the European parliament, described recent events as “very worrisome”.

“There are lot of additional questions on the table for the prime minster of Malta,” he said, adding that Muscat had to take political responsibility with regard to the principle of an independent investigation and the rule of law.

Schembri had been facing renewed pressure after the arrest of the businessman Yorgen Fenech, with whom he had alleged business links.

Caruana Galizia, one of Malta’s best-known investigative journalists, was killed in a bomb explosion as she left her home on 16 October 2017. The murder shocked Europe and raised questions about the rule of law on the small Mediterranean island. Three men are awaiting trial for setting off the bomb, as police continue their investigation into who ordered the killing.

Melvin Theuma, a taxi driver and alleged loan shark who claims to have been a middleman in the alleged murder plot, was told last week he would be granted a presidential pardon in return for information he had given about the case.

Fenech, who resigned as head of his family business earlier this month, was apprehended while sailing away from Malta on his luxury yacht at about 5.30am on Wednesday morning.

Shortly before her death, Caruana Galizia received a massive leak of data from an energy company co-owned by Fenech. His company, Electrogas, won a concession to run a major power station from Muscat’s administration.

Investigations have revealed Fenech as the owner of a secretive offshore company, 17 Black, which Caruana Galizia was looking into at the time of her death. It was later revealed 17 Black was due to make payments to the Panama companies belonging to Mizzi and Schembri.

On Tuesday, Mizzi said: “I want to make it clear once more that I have had no association, directly or indirectly with 17 Black or Yorgen Fenech.”

Schembri and Mizzi have both previously said they had no knowledge of any connection between 17 Black and Fenech, or of any plan to receive payments connected to Fenech.

Challenged about whether he had stood by his chief of staff for too long, Muscat replied: “That is a valid opinion.”