GAZIANTEP, Turkey — An Istanbul prosecutor said Thursday that he had been removed from the investigation of corruption involving the families of high-ranking officials of the ruling Justice and Development Party.

The complaint by prosecutor Muammar Akkas, a day after three senior government ministers were forced to resign when their sons were arrested in the graft investigation, signals increasing tension between his office and longtime government leaders concerned about a scandal that threatens to topple the government.

In comments Thursday, Prime Minister Recep Tayyip Erdogan said he was the ultimate target of the investigation. “They want to reach me,” he said, according to the Hurriyet newspaper. “If they try and aim at Tayyip Erdogan through this, they will [be left empty-handed].”

Akkas issued a statement accusing the government of obstructing the execution of court orders, saying police loyal to Erdogan have refused to comply.

“By means of the police force, the judiciary was subjected to open pressure, and the execution of court orders was obstructed,” Akkas said.

“A crime has been committed throughout the chain of command…. Suspects have been allowed to take precautions, flee and tamper with the evidence,” he alleged.

Akkas said he “learned that the investigation dossier, which includes search, seizure and detention decisions, was taken from my authority without any justification being offered.”

Chief prosecutor Turan Colakkadi said Akkas was removed from the investigation because he failed to report his findings to his superiors. Over the weekend, the government issued new regulations demanding that investigators report frequently to their superiors, a move the Supreme Board of Judges and Prosecutors said was unconstitutional.

The newspaper Radikal published an article Thursday quoting what it said was the full text of a subpoena issued by Akkas to Erdogan’s son Bilal. The leaked document, Radikal said, names Bilal as a suspect in a criminal investigation and instructs him to provide testimony to Akkas.

On Wednesday, Economy Minister Zafer Caglayan, Interior Minister Muammer Guler and Environment and Urbanization Minister Erdogan Bayraktar resigned. Each has a son who has been arrested in the investigation, which has netted millions of dollars found stashed in shoe boxes, exposed sanctions-breaking deals with Iran and money laundering, and focused on bribes paid to open protected areas up to construction.

The Islamic, center-right Justice and Development Party, or AKP, came to power more than a decade ago and has overseen rapid economic growth in Turkey since a severe economic crisis, years of fiscal irresponsibility and corruption. Its rallying call was clean governance, and it promised to stamp out corruption.

The graft investigation is widely seen as part of a power struggle between supporters of the cleric Fethullah Gulen, now based in the United States, and the AKP.

The relationship between Erdogan and Gulen, who were once close allies, grew bitter in recent years as the prime minister became increasingly authoritarian and moved to close down private schools run by Gulen’s organization.

The Turkish police and judiciary include many supporters of Gulen. Erdogan has overseen a purge of more than 500 police chiefs and officers investigating high-level corruption since the scandal broke last week.