WASHINGTON (AP) — Attorney General William Barr said Wednesday he is reviewing the origins of the Trump-Russia investigation, declaring he believed the president's campaign had been spied on and wanted to make sure proper procedures were followed.

"I think spying on a political campaign is a big deal," Barr told senators at a budget hearing that, like a similar House hearing Tuesday, was dominated by questions about special counsel Robert Mueller's Russia investigation.

It was not immediately clear what "spying" Barr was referring to, but President Donald Trump's supporters have repeatedly made accusations of political bias within the FBI and seized on anti-Trump text messages sent and received by one of the lead agents involved in investigating whether the Trump campaign was colluding with Russia.

Barr, who was nominated to his post by Trump four months ago, told a Senate appropriations subcommittee that though he did not have specific evidence of wrongdoing, "I do have questions about it." His review is separate from a Justice Department inspector general investigation into the early days of the FBI's Russia probe, which Barr said he expects to conclude sometime around May or June.

"I feel that I have an obligation to ensure government power was not abused," Barr said.

Barr also said he expected to release a redacted version of Mueller's nearly 400-page report next week — a slight change from the estimate he gave Tuesday, when he said the release would be within a week.

Though he said the document will be redacted to withhold negative information about peripheral figures in the investigation, Barr said that would not apply to Trump, who is an officeholder and central to the probe.

Democrats said they were concerned that a four-page summary letter of the report's main conclusions Barr released last month portrayed the investigation's findings in an overly favorable way for Trump. The letter said that Mueller did not find a criminal conspiracy between Russia and Trump associates around the time of the 2016 election and that Barr did not believe the evidence in the report was sufficient to prove the president had obstructed justice.

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Associated Press writers Chad Day, Michael Balsamo, Laurie Kellman and Matthew Daly contributed to this report.