US armed forces in Iraq uncovered a field containing 50 Iranian-made rocket launchers, all aimed at a US army base, Israel Radio reported overnight Saturday. The discovery came after an explosively formed penetrator - a high-tech device that the US military believes is smuggled from Iran - was used against US forces in the Baghdad area earlier Saturday. The penetrator was one of several bombs used in an attack that killed two American soldiers in the Iraqi capital. The Iranians deny the charge. Meanwhile, Iraqi Prime Minister Nouri al-Maliki shrugged off US doubts of his government's military and political progress, 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 an American laboratory." Al-Maliki sought to display confidence at a time when pressure is mounting in the US Congress for a speedy withdrawal of American forces. On Thursday, the House passed a measure calling for the US 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 Saturday, 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 US 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 US 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 US commander, Gen. David Petraeus, who he said works along a "purely American vision." "There are disagreements that the strategy that Petraeus is following might succeed in confronting al-Qaida in the early period but it will leave Iraq an armed nation, an armed society and militias," al-Suneid said. Al-Suneid's comments were a rare show of frustration toward the Americans from within al-Maliki's inner circle as the prime minister struggles to overcome deep divisions between Shiite, Sunni and Kurdish members of his coalition and enact the US-drawn list of benchmarks. But the US focus on the benchmarks has rankled the deep sense of Iraqi pride, even among those who share the goals set forth by the Americans. US forces have been waging intensified security crackdowns in Baghdad and areas to the north and south for nearly a month. The goal is to bring calm to the capital while al-Maliki enacts the political reforms, intended to give Sunni Arabs a greater role in the government and political process, lessening support for the insurgency. But the benchmarks have been blocked by divisions among Shiite, Sunni and Kurdish leaders. In August, the parliament is taking a one-month vacation - a shorter break than the usual two months, but still enough to anger some in the US Congress who say lawmakers should push through reforms while American soldiers are dying. In other violence, a car bomb leveled a two-story apartment building and a suicide bomber plowed his explosives-packed vehicle into a line of cars at a gas station. The two attacks killed at least eight people, police said. Also Saturday, the US military said it captured an alleged high-level al-Qaida in Iraq cell leader at Baghdad's international airport. The suspect, believed to have organized mortar and roadside bomb attacks in the capital and nearby area, surrendered "without a struggle," the military said in a statement. It did not give details on the suspect or say whether he was traveling in or out of the country when seized. The Reuters news agency said one of its Iraqi translators was shot to death in Baghdad on Wednesday along with two of his brothers, apparent victims of sectarian death squads. He was the third employee of the news agency killed in Baghdad this week. An Iraqi reporter for The New York Times, Khalid W. Hassan, was killed by gunmen Friday as he drove to work in southern Baghdad.