A suicide bomber breached Baghdad's heavy security presence again Thursday, killing a dozen people in a mostly Shi'ite district a day after more than 230 people died in one of the war's deadliest episodes of violence. Prime Minister Nouri al-Maliki called the violence in Baghdad an "open battle" nine weeks into a US-led effort to pacify the capital's streets. Despite new barricades and checkpoints erected as part of the security crackdown, a fraction of the cars in Baghdad, a city of six million residents, are searched at all. Many of the suicide car bombs explode at the checkpoints, either targeting Iraqi troops or detonating a moment before they are discovered. Some residents have suggested that Sunni insurgents have secretly stockpiled explosives in Shi'ite areas, and are now rigging their cars with bombs very close to their targets, to avoid driving long distances and risking security checks. Thursday's bomber struck within half a kilometer of Iraqi President Jalal Talabani's home in the mostly Shiite Karradah district where one of Wednesday's bombs exploded. Talabani was not believed to have been the target. The bombing killed at least 12 people and wounded 34, police said. Two Iraqi soldiers were among the fatalities. The US military on Thursday announced three more troop deaths - two soldiers killed Wednesday by a roadside bomb north of Baghdad, and another soldier killed the same day in a small arms fire attack in a southwestern area of the capital. With several thousand US soldiers still expected to arrive in Iraq and US commanders urging patience, the Baghdad security plan was already showing signs of weakness. One week ago, a suicide bomber slipped through barriers around the US-guarded Green Zone, killing an Iraqi lawmaker inside the parliament building. The same day, a truck bomber collapsed a landmark bridge across the Tigris River, killing 11 people and sending cars careening into the water. Thursday's bombing hit hours before US Defense Secretary Robert Gates arrived on an unannounced visit, saying he planned to tell Iraqi leaders that America's commitment to a military buildup in the country was not open-ended. "It is an open battle and will not be the last in the war we are fighting for the sake of the nation, dignity, honor and the people," al-Maliki said in a speech at a ceremony marking the 50th anniversary of the founding his Islamic Dawa Party. "They (attackers) have proven their spite by targeting humanity." Meanwhile, grieving relatives retrieved bodies from hospital morgues and passers-by gawked at the giant crater left by a market bomb in one of Wednesday's four attacks. Many of the more than 230 Iraqis killed or found dead nationwide were buried in quiet ceremonies before Thursday's noon prayer, according to Muslim tradition. US military spokesman Maj. Gen. William Caldwell said that al-Qaida in Iraq was suspected in the bombing. "Initial indications based on intelligence sources show that it was linked to al-Qaida," Caldwell said in a late-night telephone interview. Speaking to reporters in Israel just before flying to Baghdad on an unannounced visit, Gates said the ongoing debate in Washington about financing the war in Iraq has sent the message that both the US government and the American public are running out patience. "I would like to see faster progress," he said, adding that momentum by the Iraqi government on political reconciliation as well as legislation on sharing oil revenue sharing would "begin the process to send a message that the leaders are beginning to work together." He said that, in turn, would create an environment in which violence could begin to be reduced. Gates' visit to Iraq, his third since taking over as defense secretary in December, came a day after President Bush met congressional leaders to discuss the impasse over legislation to provide funds for the war effort in Iraq and Afghanistan. Gates said he has had no discussions with the White House about an absolute deadline by which the Pentagon must get additional funding to be able to maintain the mission.