Bombings killed seven U.S. soldiers in Baghdad and a southern city, the U.S. military said Sunday, and the country's Sunni vice president spoke out against a proposed oil law, clouding the future of a key benchmark for assuring continued U.S. support for the government.

Six of the soldiers were killed Saturday in a bombing in western Baghdad, the military said in a statement. Their interpreter was also killed.

The other soldier died in a blast Saturday in Diwaniyah, a mostly Shiite city 80 miles south of the capital where radical Shiite militias operate. Two soldiers were wounded in that attack, the military said.

Those deaths brought the number of American troops killed in Iraq since Friday to at least 15 — eight of them in Baghdad. So far, at least 71 U.S. forces have died in Iraq this month — most of them from bombs.

Elsewhere, several explosions were heard from the area around the Green Zone in central Baghdad, but it was unclear if any were inside the U.S.-controlled area, which has increasingly come under mortar and rocket fire. The American military referred questions about the explosions to the U.S. Embassy, which did not respond.

In recent months, U.S. officials have been stepping up pressure on Iraq's religiously and ethnically based parties to reach agreements on a range of political and economic initiatives to encourage national reconciliation and bring an end to the fighting.

Progress in meeting those benchmarks is considered crucial to continued U.S. support for Prime Minister Nouri al-Maliki's government at a time when Democrats in Congress are pressing for an end to the war. Those benchmarks include enactment of a new law to manage the country's vast oil wealth and distribute revenues among the various groups.

But prospects for quick approval received a setback Sunday when the country's Sunni vice president told reporters in Jordan that the proposed legislation gives too many concessions to foreign oil companies.

"We disagree with the production sharing agreement," Tariq al-Hashemi told reporters on the sidelines of an international conference hosted by the Geneva-based World Economic Forum. "We want foreign oil companies, and we have to lure them into Iraq to learn from their expertise and acquire their technology, but we shouldn't give them big privileges."

The bill also faces opposition from the Kurds, who have demanded greater control of oil fields in Kurdish areas. Kurdish parties control 58 of the 275 parliament seats.

Iraq's Cabinet signed off on the oil bill in February and sent it to parliament, a move that the Bush administration hailed as a major sign of political progress in Iraq. But parliament has yet to consider the legislation.

Al-Hashemi is among three leaders of a Sunni bloc that controls 44 seats. Together, the Kurds and the Sunnis have enough legislative muscle to delay passage of the measure, which is likely to draw opposition from some Shiite lawmakers, too.

In another political setback, the leader of Iraq's largest Shiite party, Abdul-Aziz al-Hakim, has been diagnosed with lung cancer and was headed to Iran for treatment, party officials said Sunday. Al-Hakim's absence is likely to create disarray in his Supreme Islamic Council in Iraq — a Shiite party the U.S. is counting on to push through benchmark reforms.

News of al-Hakim's diagnosis came only hours after another top Iraqi leader, President Jalal Talabani, flew to the U.S. for a medical checkup. The 73-year-old Kurdish leader was hospitalized in Jordan three months ago after collapsing.

Talabani has played an important role in trying to bridge the gap between Sunni Arabs and Shiites, and his absence is also likely to complicate efforts to forge national unity.

In the latest violence, at least 55 people were killed or found dead Sunday, including 24 people found slain execution-style in Baghdad. Nineteen of them were recovered in western areas of Baghdad, where the U.S.-led security crackdown has failed so far to halt sectarian death squads.

A suicide bomber exploded a tanker truck near an Iraqi police checkpoint outside a market west of Baghdad, killing at least two officers and injuring nine people, police said. Police said they suspected chlorine gas was used in the attack in a town just outside the turbulent city of Ramadi, 70 miles west of Baghdad. But the U.S. military said it had no reports chlorine was used.

A bomb planted under a parked car exploded near a Shiite mosque in the central Baghdad neighborhood of Bab al-Sharji, police said. The blast killed two civilians, wounded 10 and damaged nearby houses and the mosque, police said.

Several hours later, a mortar shell landed in a commercial area in central Baghdad, killing one person and wounding three, police said.

Also Sunday, a U.S. spokesman said troops killed a Shiite extremist believed to have masterminded a brazen January attack in Karbala in which four U.S. soldiers were killed.

Azhar al-Duleimi was killed Friday in a raid in north Baghdad, Maj. Gen., William Caldwell told a cable news network. Caldwell said U.S. troops had been pursuing al-Duleimi "relentlessly" since the Jan. 20 attack, in which English-speaking gunmen wearing U.S. military uniforms and carrying American weapons attacked a joint military command headquarters in Karbala.

The attackers killed one soldier and abducted four others, later shooting them all to death.

"You know, anybody who kidnaps an American soldier and murders them, we're going to continue to hunt down. And that's exactly what we've been doing with this guy," Caldwell said of al-Duleimi.

Caldwell spoke as thousands of soldiers continue their search for three comrades abducted in a May 12 ambush south of Baghdad. Four other U.S. soldiers and one Iraqi were killed.

Meanwhile, two U.S. Republican senators said Sunday at the conference in Jordan that the U.S. has evidence Iran sent weapons and trainers to instruct militants in Iraq to carry out terror attacks there.

Sen. Orrin Hatch of Utah told a panel discussion on Iraq's future that during a trip last week to Iraq, he saw "evidence that Iran was supplying weapons and bomb-making components to Iraqi terrorists."

A former Iranian government official, who was on the same panel as Hatch, denied the claims, saying his country was falling prey to a "barrage of accusations" from the U.S. since the Islamic revolution in 1979.

"Iraq is already so full of arms that it doesn't need arms from Iran," said hard-liner Mohammed J.A. Larijani, a former deputy foreign minister and brother to Iran's top nuclear negotiator, Ali Larijani.

But Sen. Gordon Smith of Oregon told the same panel he saw "confiscated Iranian weapons" and captured Iranians who confessed to a mission to train Iraqi extremists in military tactics.

Neither senator elaborated on their claims.