BAGHDAD — Prime Minister Nouri al-Maliki shrugged off U.S. doubts of his government's military and political progress on Saturday, saying Iraqi forces are capable and American troops can leave "any time they want."

One of his top aides, meanwhile, accused the United States of embarrassing the Iraqi government by violating human rights and treating his country like an "experiment in a U.S. lab."

Al-Maliki sought to display confidence at a time when pressure is mounting in Congress for a speedy withdrawal of U.S. forces. On Thursday, the House passed a measure calling for the United States to withdraw its troops by spring, hours after the White House reported mixed progress by the Iraqi government toward meeting 18 benchmarks.

During a press conference, al-Maliki shrugged off the progress report, saying that difficulty in enacting the reforms was "natural" given Iraq's turmoil.

"We are not talking about a government in a stable political environment but one in the shadow of huge challenges," al-Maliki said.

"So when we talk about the presence of some negative points in the political process, that's fairly natural."

Al-Maliki said his government needs "time and effort" to enact the political reforms that Washington seeks — "particularly since the political process is facing security, economic and services pressures, as well as regional and international interference."

But he said if necessary, Iraqi police and soldiers could fill the void left by the departure of coalition forces.

"We say in full confidence that we are able, God willing, to take the responsibility completely in running the security file if the international forces withdraw at any time they want," he said.

One of al-Maliki's close advisers, Shiite lawmaker Hassan al-Suneid, bristled over the American pressure, telling The Associated Press that "the situation looks as if it is an experiment in an American laboratory (judging) whether we succeed or fail."

He sharply criticized the U.S. military, saying it was committing human rights violations and embarrassing the Iraqi government through such tactics as building a wall around Baghdad's Sunni neighborhood of Azamiyah and launching repeated raids on suspected Shiite militiamen in the capital's slum of Sadr City.

He also criticized U.S. overtures to Sunni groups in Anbar and Diyala provinces, encouraging former insurgents to join the fight against al-Qaida in Iraq. "These are gangs of killers," he said.

In addition, he said that al-Maliki has problems with the top U.S. commander, Gen. David Petraeus, who he said works along a "purely American vision."