Insurgents in Iraq launched two days of bloody assaults at the start of the Muslim holy month of Ramadan that left at least 31 people dead, most of them members of the security forces serving in restive Sunni-dominated areas, authorities said Thursday.

The killings are the latest in a wave of bloodshed that has killed more than 2,600 people since the start of April. The months-long eruption of violence — Iraq’s worst in half a decade — is raising fears that a civil war between the country’s Sunnis and Shiites is again imminent.

The deadliest of the latest attacks occurred at sundown Wednesday as Iraqis marked the end of the first day of Ramadan fasting, though authorities provided details only the following morning.

Gunmen struck at an army checkpoint near Barwana, which lies across the Euphrates River from the town of Haditha, about 140 miles northwest of Baghdad in the mainly Sunni province of Anbar. Barwana’s mayor, Meyasser Abdul-Mohsin, said three soldiers were killed.

The attackers then made their way to a nearby trailer used by special oil-industry police assigned to protect a pipeline. The men inside were sitting down to break the Ramadan fast at sunset, Abdul-Mohsin said.

The gunmen shot up the trailer and then set it on fire, the mayor said. Eleven police officers were killed, he said.

Exxon Mobil, BP and other international oil firms have flocked to Iraq since the 2003 U.S.-led invasion to capitalize on the country’s vast oil wealth. Iraq is now the second-largest producer in Organization of the Petroleum Exporting Countries, after Saudi Arabia, and oil revenue accounts for 95 percent of its budget.

Insurgents unleashed more attacks Thursday. A police station in Ramadi, the capital of Anbar, was the target of a morning assault that left two officers dead, provincial officials said. Later, militants staged a car-bomb and gunfire assault on police headquarters in Fallujah, also in Anbar province, killing seven officers. A roadside bombing in central Fallujah killed another police officer.

Anbar has been the center of months of protests by Iraq’s minority Sunnis over what they perceive as second-class treatment by the Shiite-dominated government. Sunni militant groups have tried to tap into that anger and link their cause with that of the protesters.

In other violence, a car bomb rocked Baghdad’s commercial district of Karrada late Thursday afternoon, killing two police officers and two civilians, and gunmen in speeding cars fatally shot an off-duty soldier and a civilian in separate attacks in the northern city of Mosul. Elsewhere in Mosul, a police officer was killed in a roadside bombing.

Bombers also struck in the northern cities of Tuz Khormato and Kirkuk, injuring dozens, officials said.

— Associated Press