BAGHDAD -- Four Iranian pilgrims and an Iraqi were killed on Monday when a car bomb exploded next to their bus north of Baghdad, said Iraqi officials.
The bus was on the highway just outside the town of Muqdadiyah headed towards the capital Baghdad 60 miles (90 kilometers) away when the car exploded. Nine other Iranians on the bus were injured.
There is a steady flow of Iranian pilgrims into Iraq to visit its hallowed Shiite shrines and they are often targeted by Sunni militants, especially in former insurgent strongholds like Diyala province where the attack took place.
The U.S. military in Iraq, meanwhile, provided further details about a brazen robbery of four foreign commercial ships anchored of Iraq's southern coast last week.
Iraqi naval authorities chased the assault rifle-wielding bandits up the Shatt al-Arab waterway leading from the Persian Gulf, "resulting in the capture of one of the getaway boats, a portion of the stolen goods, and the arrest of two suspects," said the statement.
The seaborne robbery -- which occurred in an area patrolled jointly by the U.S. and Iraqi navies -- raised concern concerns that insurgents could threaten the waterway.
But Iraqi officials insisted thieves and not insurgents were behind the bold robberies, which they said do not pose a larger threat to commercial traffic in the strategic Persian Gulf waters.
"The situation is under control and we don't believe that there will be (further) ... activities that threaten trade," said Ammar al-Mousawi, a spokesman for the Iraqi force protecting the country's oil and gas facilities.
On Sunday, the U.S. Navy said that gunmen armed with AK-47 rifles had boarded four commercial ships near Umm Qasr port over a two-hour time span on Aug. 8. The assailants took computers, cell phones and money from crew members before fleeing.
The vessels attacked were identified as the American ship Sagamore, the Antigua-flagged Armenia, the North Korean Crystal Wave and the Syrian Sana Star.
A Basra-based intelligence officer, speaking on condition of anonymity because the investigation was ongoing, said the interrogation of two Iraqis arrested after the incident indicated it was a robbery attempt without a larger agenda.
Basra, Iraq's second-largest city, which is located near Umm Qasr, has been relatively quiet since a 2008 military crackdown that ended three years of Shiite militia rule, rampant crime and turmoil. The area and the surrounding province contain about 70 percent of Iraq's proven oil reserves of 115 billion barrels.
Insurgents have warned they would step up attacks ahead of U.S. plans to end its combat mission by September, a step toward a deadline for a full military withdrawal by the end of next year.
The drawdown to bring the number of American soldiers in Iraq to 50,000 by the end of the month continues, despite the country's political impasse following the March 7 parliament elections, which produced no clear winner.
In a sign of growing frustration over the lack of any political compromise five months after former prime minister Ayad Allawi narrowly defeated Iraq's current leader, Nouri al-Maliki, four activist groups said Monday they had filed a lawsuit against acting parliament speaker Fouad Massoum.
The groups accuse Massoum of violating the constitution by ruling that the newly elected parliament, which convened June 14, would remain in an open-ended session until a political agreement is reached. The decision has perpetuated the political stalemate by delaying key steps the lawmakers were required to make, such as choosing a new president and speaker, the suit charges.
Massoum acknowledged the constitution has been violated, but told The Associated Press he will defend his decision in court. The lawsuit was filed Aug. 9 with Iraq's Federal Supreme Court by groups that include women's and workers' rights organizations.