The White House said Monday it plans to query Iraqi Prime Minister Nouri al-Maliki's government about reports that some of his people are behind a purge of security officers who have acted too aggressively against Shiite militias.

"We are aware of the reports and we're concerned about them and that will be the focus of conversations," White House spokesman Tony Snow said.

At least 16 army and national police commanders have been fired, detained or pressured to resign since March 1, The Washington Post reported Monday, citing U.S. military documents. Nine were Sunnis, and though some appear to have been fired for legitimate reasons, several were considered among the best in the field, the newspaper reported. A department of al-Maliki's office played a lead role in the dismissals, the Post said, citing U.S. military officials.

Officials close to al-Maliki denied the allegations.

Al-Maliki's government is dominated by Iraq's Shiite majority. But he promised, as a part of Bush's ordering of additional U.S. troops to Iraq, to not only pursue the Sunni-led insurgency but also to crack down on violent Shiite militias that have terrorized Sunnis, particularly in Baghdad.

Sunnis are in the minority Iraq, but held the reins of power under Saddam Hussein's regime. Al-Maliki had been criticized during previous security crackdowns for ignoring violent Shiite groups such as one led by radical Shiite cleric Muqtada al-Sadr, a key political supporter of the prime minister.

"It is vital for the success of an Iraqi democracy to have security forces that will enforce the law fairly, regardless of who you are or regardless what group you belong to," Snow said.

But Snow defended the performance of al-Maliki and his government.

"There has been aggressive action within Baghdad, in Shia neighborhoods," he said. "Keep in mind we are not yet halfway into full deployment in the Baghdad security plan."

The questions about al-Maliki's performance come at a crucial time in Washington.

Congress is expected to send Bush a bill funding the Iraq war on Tuesday. Democratic aides said they anticipate Bush will veto the bill on Wednesday, before a scheduled meeting at the White House between Bush and bipartisan congressional leaders, including House Speaker Nancy Pelosi, D-Calif., and Senate Majority Leader Harry Reid, D-Nev.

Bush has promised to veto the funding legislation because it includes a requirement that Bush begin withdrawing American troops from Iraq on Oct. 1. He opposes any such deadlines or targets.

Even so, House Democrats say they might schedule a vote for Wednesday to try to override Bush's veto. While the vote would fail, the move would show Democrats were exhausting their options in trying to challenge the president.

After the veto, Democrats will likely drop the withdrawal timetable and may replace it with conditioning U.S. support on the Iraqi government meeting certain benchmarks.

This tact may solicit a second veto threat from Bush. Secretary of State Condoleezza Rice said Sunday that the president wouldn't sign any war spending bill that penalizes Iraq's government for failing to make progress on promises to equitably distribute oil wealth, refine its constitution and expand democratic participation.

Bush laid out so-called benchmarks for Iraq's government to meet when he called for the extra U.S. troops. But he attached no consequences if they were not met, and no timeline for them to be accomplished.

He has said that the Iraqi government knows it does not have unlimited patience from either the U.S. or its own citizens. The president says this is incentive enough for al-Maliki's government to perform, and that Washington cannot dictate to a sovereign nation how it governs.