The Justice Department’s independent inspector general opened an inquiry on Friday into the Trump administration’s secret seizure of data from House Democrats and reporters as prosecutors sought to hunt down the sources of leaks of classified information.

In a statement, Michael E. Horowitz, the inspector general, announced he would review the department’s use of subpoenas and other legal maneuvers to secretly access communications records of Democratic lawmakers, aides, and at least one family member, which was first reported on Thursday by The New York Times.

Mr. Horowitz also said he will look at other recently disclosed actions to secretly seize data about reporters. The Biden Justice Department in recent weeks has disclosed that prosecutors during the Trump administration also sought and obtained phone records for journalists at The Washington Post, CNN, and The New York Times and then sought to stop the information from becoming public.

“The review will examine the department’s compliance with applicable D.O.J. policies and procedures, and whether any such uses, or the investigations, were based upon improper considerations,” Mr. Horowitz said.

Hours earlier, top Senate Democrats had also announced that they would open their own investigation into the Trump Justice Department’s decision to go after records associated with Congress. They demanded public testimony from former Attorney General William P. Barr and other Justice Department officials.

“This issue should not be partisan; under the Constitution, Congress is a coequal branch of government and must be protected from an overreaching executive, and we expect that our Republican colleagues will join us in getting to the bottom of this serious matter,” said Senator Chuck Schumer of New York, the majority leader, and Senator Richard J. Durbin of Illinois, the chairman of the Senate Judiciary Committee.

They called on Republicans to join them in demanding answers, but so far none have.

Mr. Horowitz’s announcement followed a referral by the deputy attorney general, Lisa O. Monaco, according to a senior Justice Department official. House Speaker Nancy Pelosi also called for an inspector general investigation.

The two investigations came as Democrats and privacy advocates decried the seizures and aggressive investigative tactics as a gross abuse of power to target another branch of government. They said the pursuit of information on some of President Donald J. Trump’s most visible political adversaries in Congress smacked of dangerous politicization.

The Times reported that as it hunted for the source of leaks about Trump associates and Russia, the Justice Department had used grand jury subpoenas to compel Apple and one other service provider to hand over data tied to at least a dozen people associated with the House Intelligence Committee beginning in 2017 and 2018. The department then secured a gag order to keep it secret.

Though leak investigations are routine, current and former officials at the Justice Department and in Congress said seizing data on lawmakers is nearly unheard-of outside of corruption investigations. The Times also reported that after an initial round of scrutiny did not turn up evidence tying the intelligence committee to the leaks, Mr. Barr objected to closing out the inquiry and helped revive it.

Investigators gained access to the records of Representative Adam B. Schiff of California, the top Democrat on the committee and now its chairman; Representative Eric Swalwell of California; committee staff aides; and family members of lawmakers and aides, including one who was a minor.

“I hope every prosecutor who was involved in this is thrown out of the department,” Mr. Swalwell said in an interview on Friday. “It crosses the line of what we do in this country.”