BAGHDAD - A wave of car-bomb blasts tore through Shiite areas south of Baghdad on Monday, killing at least 36 and deepening fears that Iraq is rapidly spiraling back out of control.

The attacks capped a week of turmoil that is posing the greatest test of Iraq’s stability since U.S. troops left the country in late 2011. At least 218 people have been killed in attacks and battles between gunmen and security forces that began with clashes at a Sunni protest camp in northern Iraq on April 23.

The unrest follows four months of widespread protests among those in Iraq’s Sunni minority, who feel they are discriminated against and are being marginalized by Prime Minister Nouri al-Maliki’s Shiite-led government.

Iraqi officials fear that Sunni feelings of disenfranchisement could be exploited by extremist groups such as al-Qaida and militant organizations such as the Naqshabandi Army, which is linked to Saddam Hussein’s former regime.

In a possible sign of mounting worries over the deteriorating security situation, Iraqi authorities announced they plan to close the country’s only border crossing with Jordan, beginning today. The Interior Ministry said the move is related to Iraq’s domestic affairs.

The route to the border runs through the cities of Ramadi and Fallujah, west of Baghdad, which have been hotbeds of Sunni anger at the government. Many Sunnis in western Iraq have economic, tribal and cultural ties with Jordanians, most of whom are also Sunni.

Iraqi security forces had surrounded Ramadi and Fallujah demanding that the area’s tribes hand over those responsible for killing five Iraqi soldiers over the weekend. Authorities gave the tribes 48 hours.

The deadline passed, but Jaber Jabri, a member of the parliament from Ramadi, said late Monday that a tentative deal had been struck to defuse the situation. He said a committee of military commanders, local officials and tribal figures would search for those thought to be responsible, and the tribes would remove their guns from the streets of Ramadi.

The army would be allowed to search specific areas for weapons but would not launch an attack, he said, adding, “I hope now the situation will get better.”

Sheik Fakhir al-Kubaisi, a protest organizer in Anbar province, blasted the latest closure plans as “another escalation by the Iraqi government to punish the revolting Iraqi people.” He predicted the closure would drive up the prices of food and medicine, and might be tied to a coming security crackdown on protest sites in the area.

The Interior Ministry spokesman, Lt. Col. Saad Maan Ibrahim, insisted the border closure was solely a technical matter and is unrelated to ongoing tensions in the country. He did not elaborate and said it should reopen within 48 hours.

Iraq temporarily shut the same border crossing in January, weeks after anti-government protests broke out along the desert highway heading to the checkpoint. That angered many Sunnis in western Iraq, who saw it as collective punishment for their rallies.

The International Crisis Group recently warned that the standoff between Sunni protesters and the central government has begun a dangerous slide toward confrontation.

“The emergence of an arc of instability and conflict linking Lebanon, Syria and Iraq, fueled by sectarianism and involving porous borders as well as cross-border alliances, represents a huge risk,” the conflict-prevention group warned. “Failure to integrate Sunni Arabs into a genuinely representative political system in Baghdad risks turning Iraq’s domestic crisis into a broader regional struggle.”

Monday’s deadliest attack struck the southern city of Amarah. Two parked cars loaded with explosives went off simultaneously in the early morning near a gathering of construction workers and a market, killing 18 people and wounding 42, the police said.

That attack was followed by another parked-car bombing near a restaurant in the city of Diwaniyah that killed nine people and wounded 23. At least three cars were left charred and twisted from the blast outside a two-story building, and its facade was damaged. Shop owners and cleaners brushed debris off the bloodstained pavement.

Amarah, some 200 miles southeast of Baghdad, and Diwaniyah, 80 miles south of the capital, are heavily Shiite and usually peaceful.

Hours later, yet another car bomb went off in the Shiite holy city of Karbala, killing three civilians and wounding 14, police said. Two early Islamic figures revered by Shiites are buried in the city, about 55 miles south of Baghdad.

And in the otherwise predominantly Sunni town of Mahmoudiya, about 20 miles south of Baghdad, a car bomb ripped through a Shiite neighborhood, killing six people and wounding 14, another police officer said.

Ibrahim Ali, a schoolteacher there, was teaching a class when a thunderous boom went off.

“The students were panicking and some of them started to cry,” he said, recounting the sight of burned bodies and cars on fire at the nearby blast site. “We have been expecting this violence against Shiites because of the rising sectarian tension in the country.”

Medical officials confirmed the casualty figures.

No one immediately claimed responsibility for Monday’s blasts. But coordinated bombings in civilian areas are a favorite tactic for al-Qaida in Iraq.

Parliament speaker Osama al-Nujaifi, a Sunni, condemned Monday’s bombings and urged the government to step down “in order to save the country from the specter of civil war and sectarian strife.” He called for the installation of an interim government, dissolution of the parliament and early elections.

He issued a similar call in February for the prime minister to step down and for early elections, but there is little sign for now of that happening.

Sectarian violence has spiked since April 23, when security forces tried to make arrests at a Sunni Muslim protest camp in the northern city of Hawija. The move set off a clash that killed 23 people, including three soldiers.

In Baghdad, al-Maliki met on Monday with the prime minister of Iraq’s largely autonomous Kurdish region, Nechirvan Barzani.

A statement from the Iraqi leader’s office said the two sides discussed their differences “in an atmosphere of frankness and seriousness and with a common desire to find solutions.”

Ongoing disputes between Baghdad and the Kurds over sensitive issues such as ethnically disputed territories and how to manage the country’s vast oil wealth further undermine Iraq’s stability as al-Maliki tries to manage relations with the country’s Sunni Arabs.

In other violence Monday, several mortar shells exploded in an uninhabited area near Baghdad International Airport around sunset, but no casualties were reported, police said.

An Iranian exile group whose members live in a refugee camp near the airport described the explosions as rocket strikes. It said they hit water canals at the southern part of the camp.

The group, the National Council of Resistance of Iran, has been pushing for camp residents, members of its Mujahedeen-e-Khalq militant wing, to be moved back to another camp north of Baghdad. Iraq’s government wants them out of the country altogether.

Information for this article was contributed by Adam Schreck, Sinan Salaheddin and Sameer N. Yacoub of The Associated Press; and by Ned Parker of the Los Angeles Times.

Front Section, Pages 1 on 04/30/2013