Baghdad, Iraq ? For the second time in less than a week, a group of U.S. senators met Saturday with Iraqi leaders to warn that American interest in stabilizing the country could dwindle unless they speed up work to form a unity government.

“This issue needs to be resolved, not only quickly but also inclusively,” Sen. John McCain said as Iraqi President Jalal Talabani, standing beside him, nodded in agreement.

The Arizona Republican, who backed the 2003 U.S.-led invasion to topple Saddam Hussein, said later he believed Iraqis “understand the sense of urgency we have conveyed to them.”

“We all know the polls show declining support among the American people,” McCain added.

As his delegation left a lunch at Talabani’s villa, heavily armed convoys arrived, bringing leaders of Iraq’s main political blocs to another round of wrangling over priorities and procedural rules for a new government. Later they reported progress, but cautioned that the task was complex.

Political violence claimed at least 20 lives across the country Saturday. The bloodiest attack occurred in Mahmoudiyah, 30 miles south of Baghdad, where insurgent mortars apparently aimed at an Iraqi army base hit a nearby neighborhood and mosque, killing four civilians and wounding 13.

In Baghdad, a bomb explosion in a vacant traffic police booth killed four people on a passing minibus.

The day’s casualties also included victims of apparent sectarian attacks, a Sunni Muslim imam who had stopped on a Baghdad street to repair his car and two men found with hands and feet tied and bullet wounds in the head.

Iraqi President Jalal Talabani, right, gives a joint news conference with U.S. Republican Sen. John McCain Saturday in Baghdad, Iraq. McCain urged Iraqis to form a new government quickly.

Speaking at a community sports center during the day, U.S. Ambassador Zalmay Khalilzad told Iraqi athletes that the violence “threatens to rip Iraq apart.” He called the effort to form a government “a defining moment.” Iraq’s ethnic and sectarian political factions have been deadlocked in that effort since the Dec. 15 election left none with a majority in parliament.

One obstacle has been resistance to the dominant Shiite Muslim bloc’s nomination of interim Prime Minister Ibrahim al-Jaafari to keep his job. Another is distrust among the Shiite, Sunni Arab, Kurdish and secular political factions.

Facing vocal criticism from U.S. officials and ordinary Iraqis, factional leaders have met several times over the past two weeks and reported some progress. Last Sunday they agreed to create a 19-member council representing all the main factions to guide the new government’s policies. Friday they settled a dispute over the council’s authority by deciding that its decisions would not be binding on the prime minister or his Cabinet.

Saturday’s talks focused on principles for the government, a formula for giving each faction a share of Cabinet seats, and a procedure for reaching Cabinet decisions.

The most explosive issue for the new government is how to curb Shiite militias. Some of them operate from within the police force, and they are accused of killing hundreds of unarmed Sunnis in sectarian attacks. The principles being studied in the negotiations includes a commitment to dissolve those militias.

The U.S. delegation included two other senators, three House members, and three governors. A separate delegation of six senators visited Iraq on Tuesday.

Asked by reporters whether the U.S. visitors had brought helpful advice for breaking the stalemate, Talabani said: “Only friendly words like, ‘Please hurry up.”‘