Gunmen ambushed travelers on a highway leading from Baghdad to Shiite areas to the south on Tuesday, killing 14 people, while mortar rounds slammed into an area near the Iraqi prime minister's office in the U.S.-controlled Green Zone in the capital, a government official said.

The attacks against the travelers began at 6:45 a.m., when gunmen took aim at a minibus, killing 11 Shiites and wounding three, as it passed near Iskandariyah, 30 miles south of Baghdad in a predominantly Sunni area dubbed the "Triangle of Death" because of frequent insurgent violence.

About 45 minutes later, a group of gunmen standing on the highway opened fire at civilian cars, killing three people and wounding five near Latifiyah and about 6 miles north of the site of the initial attack.

Complete coverage is available in FOXNews.com's Iraq Center.

The attacks occurred on the main highway linking the capital to predominantly Shiite southern provinces. Farmers often use the road to transport goods and Shiite pilgrims use it for treks to the holy cities of Najaf and Karbala, but they have to go through the dangerous areas closer to Baghdad.

No casualties were reported in the mortar attack — the second strike against the sprawling complex in about 12 hours — but it underscored heightened concerns about security in an area that is home to the U.S. and British embassies and thousands of American troops, as well as the Iraqi government headquarters.

The chief government spokesman Ali al-Dabbagh, meanwhile, said Iraqi officials have received reports that the leader of Al Qaeda in Iraq, Abu Ayyub al-Masri, was killed by Sunni tribesmen but the information has not been confirmed.

The U.S. military said it was still looking into the reports amid a series of conflicting statements by other Iraqi officials on the subject. Iraqi officials have released similar reports in the past, only to acknowledge later they were inaccurate.

The first round of explosions in the Green Zone occurred about at 10 p.m. Monday and another round struck at about 10 a.m. Tuesday.

U.S. military spokesman Lt. Col. Christopher Garver said no military personnel were injured in Monday's strike. He said the explosions on Tuesday were still under investigation, although "indications appear it was indirect fire," the term used by the military for rocket or mortar attacks.

An Iraqi government official, speaking on condition of anonymity because of the sensitivity in discussing security issues, said six mortar rounds fell around the offices of Prime Minister Nouri al-Maliki on Tuesday and the closest came with 100 yards of the compound. The explosions late Monday also were directed toward that part of the Green Zone, also known as the international zone, the official said.

Insurgents and militia fighters routinely fire rockets and mortars into the Green Zone, which houses the U.S. and British embassies, the Iraqi government headquarters and thousands of American troops on the west bank of the Tigris River.

The attacks seldom cause casualties or damage because they are poorly aimed and the 4-square-mile zone contains much open space. But concerns have been heightened after two Americans — a contractor and a soldier — were killed in late March in a rocket attack on the area and two suicide vests were found unexploded less than a week after that.

The adequacy of security in the vast area in central Baghdad more recently came into question in the aftermath of the April 12 suicide bombing in the Iraqi parliament building's dining hall. One lawmaker was killed in the blast, which was claimed by an Al Qaeda-led amalgam of Sunni insurgents.

Complete coverage is available in FOXNews.com's Iraq Center.

The Pentagon also said Monday that documents captured in recent fighting in Baghdad included two identity cards for access to the Green Zone and an ID card for access to the U.S. Embassy.

On the diplomatic front, a senior Iranian envoy, Ali Larijani, met with Iraq's top Shiite cleric, Grand Ayatollah Ali al-Sistani, in the holy city of Najaf, 100 miles south of Baghdad.

Larijani flew to Baghdad on Sunday for talks with Iraqi leaders ahead of this week's regional meetings in Egypt — the highest-ranking Iranian official to visit Iraq since the collapse of Saddam Hussein's regime in 2003.

Al-Maliki is hoping to shore up support for his embattled Shiite-dominated government at the conference in Sharm el-Sheik.

Iraq's Sunni Arab vice president Vice President Tariq al-Hashemi's office said Monday that he had discussed threats by Sunni ministers to leave the Shiite-dominated government during a weekend telephone conversation with President Bush.

The White House confirmed that Bush called al-Hashemi on Sunday to discuss "the current situation in Iraq" and "the importance of additional steps in the reconciliation process."

In a statement on his Web site, al-Hashemi said the call was made after his Iraqi Accordance Front, which holds 44 seats in the 275-member parliament, threatened to quit al-Maliki's Cabinet.

Bush and al-Hashemi "spoke frankly about the stumbling political process and ways of getting out of the current dilemma," the vice president's statement said. "It seems that the (Accordance) Front has lost hope for a change in the current situation."

In Washington, presidential spokesman Tony Snow said Bush "deals with leaders throughout the Iraqi government," including al-Hashemi, who visited the White House last year. Snow did not discuss the substance of the conversation.

The Front's departure from the Cabinet could plunge Iraq into a major political crisis because it would mean the end of the unity government of Shiites, Sunnis and Kurds.