The United States called Wednesday for Iraq to dismantle non-government "armed groups" that have "undermined national sovereignty" ahead of a visit to Washington by Iraqi Prime Minister Mustafa al-Kadhemi.

"Armed groups not under the full control of the prime minister have impeded our progress," said Secretary of State Mike Pompeo. "Those groups need to be replaced by local police as soon as possible."

Pompeo was speaking at a press conference in Washington together with Iraqi Foreign Minister Fuad Hussein, one day before Kadhemi meets President Donald Trump at the White House.

Pompeo did not specify which groups he was referring to, but Kadhemi, who took office in May, faces challenges from factions of the Hashed al-Shaabi, a coalition of Iraqi Shiite paramilitary groups with close ties to Iran.

His visit to Washington comes amid weekly attacks attributed to the groups against US installations and assets in the country.

Pompeo said that he had assured Husesein that the US would help Iraq toward this end.

"We talked about how the United States and Iraq can work together to make Iraq more safe and stable," he said.

Pompeo said the US is committed to supporting the official Iraqi security forces "to curb the power of militias that have for far too long terrorized the Iraqi people, and undermined Iraq's national sovereignty." 

The two countries have been conducting a "strategic dialogue" since June as the Trump administration seeks to reduce the US military presence there.

Asked about the plan for cutting the 5,000 US troops now in Iraq, Pompeo said he had no numbers and urged people "not to focus on that."

But the continuing US presence, mostly focused on fighting remnants of the Islamic State jihadist group, will be a key issue when Kadhemi meets Trump.

Hashed al-Shaabi, which maintains armed units viewed as threats by Washington, is integrated into the Iraqi state, and its political representatives have called for the expulsion of US troops.