Israeli police have accused members of Benjamin Netanyahu’s inner circle, including a relative and a former head of staff, of bribery and money laundering in relation to a controversial $2bn deal to buy German submarines and naval patrol boats.

The announcement will put added pressure on the country’s second-longest serving prime minister who has been named in three other corruption investigations, in two of which police have recommended he be indicted.

Police said on Thursday they had found sufficient evidence to charge David Shimron, Netanyahu’s personal lawyer and relative, over his role in pushing the government to buy nuclear-capable submarines.

Shimron was suspected of promoting the sale from the ThyssenKrupp corporation “while using his status and closeness to the prime minister and public officials”, police said. The lawyer had received suspicions payments amounting to 270,000 shekels (£56,000) which were defined as a “reward for success” and for “opening the doors”, police said.

The lawyer received the money from an Israeli businessman, Michael Ganor, police said, who has since turned state witness in a deal that will see him serve 12 months in prison.

Netanyahu has not been accused of any wrongdoing in the investigation, known as case 3,000, although police said in a statement that he had provided testimony in their investigation.

“I did not commit any crime,” Shimron told Israel’s YNet news website, which asked him about the police recommendations to prosecutors and posted an audio clip of his comments. Shimron’s lawyer, in a statement to Reuters, denied any wrongdoing by his client, saying he was not involved in the submarine deal.

David Sharan, a former head of staff for Netanyahu, was also accused of receiving 130,000 shekels (£27,000) for promoting the deal. Police said he had committed bribery, fraud and breach of trust, conspiracy to commit a crime, money laundering and election law offences.

Israel has been gripped by several corruption investigations related to the Netanyahu family over the past two years.

In February police recommended that the prime minister be indicted on charges of bribery and breach of trust in two of those inquiries. The first, case 1,000, related to claims he and his family received more than £210,000 in gifts including expensive cigars, pink champagne and jewellery from international billionaires.

In case 2,000, police say Netanyahu made a deal with a newspaper publisher for more sympathetic coverage in return for lowering the circulation of a rival paper.

The prime minister and his wife, Sara, have been questioned but are not suspects in a fourth investigation, case 4,000, which centres around allegations that an Israeli telecom provider was offered regulatory incentives for positive coverage in an online news website.

Netanyahu has repeatedly denied any wrongdoing in any of the cases, describing them as baseless and alleging he is the victim of a witch-hunt.

The attorney general has not yet decided whether to accept the indictment recommendations, and Netanyahu’s rightwing coalition remains popular in Israel with observers predicting a win in next year’s election.

In a separate inquiry, the premier’s wife, Sara, was charged in June with fraud and breach of trust for allegedly using tens of thousands of dollars of public funds to pay for delivery meals to the couple’s residence, despite having an official in-house chef.

If convicted, she could face a maximum sentence of five years behind bars, although that is considered unlikely. Her lawyers said the charges were “false” and “delusional”.

ThyssenKrupp said in a statement to the Guardian: “Our information comes so far only from the press, we do not yet have any confirmed information. As soon as we know all the facts, we will examine further measures within the framework of the legal possibilities.”