BAGHDAD, Iraq — Iraqi politicians struggled Saturday to reach agreement on candidates for two key security posts that remained vacant a week after Prime Minister Nouri al-Maliki's government of national unity took office.

The political maneuvering came as Iran's foreign minister visited the Shiite holy cities of Karbala and Najaf, where he met with Iraq's top Shiite cleric Grand Ayatollah Ali al-Sistani as he wrapped up the second high-level visit by an Iranian delegation since Saddam Hussein was ousted in April 2003.

Iranian Foreign Minister Manouchehr Mottaki met with al-Maliki and other top Iraqi officials on Friday, and he rejected a U.S. offer of direct talks on Iraq as Tehran hardened its position against international pressure to stop uranium enrichment.

Al-Maliki said Thursday that he could be ready soon to name the two men who will be charged with carrying out his pledge to take over security for Iraq within 18 months, but Friday passed without word of the appointments.

His spokesman, Yassin Majid, said the main Shiite, Sunni and Kurdish political blocs in the 275-member parliament would resume talks on the candidates Saturday afternoon "and probably this issue will be settled today."

Al-Maliki left the posts vacant when he formed his government last week because of ethnic and sectarian disagreements. He said earlier this week that problems included the large number of candidates presented by his Shiite United Iraqi Alliance and the Sunni Arabs' Iraqi Accordance Front and concerns about links of some nominees to the former regime.

Violence resumed Saturday as a bomb in a parked car exploded near a busy bus station in southern Baghdad, killing at least four civilians and wounding seven, police Capt. Jamil Hussein said.

Gunmen also broke into a gardening store in Baghdad and killed the Shiite owner, Ali Hussein Kadhin, a Shiite, police Lt. Maitham Abdul Razzaq said.

Both attacks occurred in the predominantly Sunni neighborhood of Dora, and came a day after bombs hit three different outdoor markets in largely Shiite areas of the capital, killing at least 18 people and wounding more than 60.

The U.S. military, meanwhile, said six terror suspects had been captured Friday in Ramadi, saying information from recent detainees led to the raid.

Residents in the volatile city, 70 miles west of Baghdad complained they had been surrounded for days without water or electricity amid recent clashes between U.S. forces and insurgents. Footage from AP Television News showed collapsed tin stalls and rubble as a fighter plane flew overhead and gunfire could be heard.

Elsewhere, a policeman was killed and an officer wounded when a roadside bomb exploded near their convoy in Baghdad's western district of Mansour, Razzaq said. He also said three policemen were wounded when gunmen ambushed a convoy of Interior Ministry commandos in the southern neighborhood of al-Bayaa in the capital.

Gunmen in three speeding cars also ambushed a patrol in western Baghdad, wounding 10 people, including six policemen, and two other policemen were injured in drive-by shootings in a nearby neighborhood, police Capt. Jamil Hussein said.