BAGHDAD (AP) -- Two bombs hidden inside air conditioners exploded Friday in a Sunni mosque packed with worshippers north of Baghdad, killing at least 18 people in the latest in a string of attacks on the sect's holy sites in Iraq.
Iraq is weathering its worst bout of violence in half a decade. Attacks have risen significantly since April, intensifying fears the country is slipping back toward the widespread bloodshed and sectarian fighting that marked the years following the 2003 U.S.-led invasion.
More than 4,000 people have been killed between April and August, U.N. figures show. Another 396 have been killed so far in September, according to an Associated Press tally.
Friday's attack took place on the outskirts of the city of Samarra. The deputy head of the municipal council there, Mizhar Fleih, said bombs were placed inside two of the Musaab Bin Omair mosque's wall-mounted air-conditioning units. In addition to the 18 killed, the explosions also wounded 21 people, he said.
"We are worried that the attacks on Sunni and Shiite mosques aim at reigniting the sectarian strife in this country," Fleih said.
Officials at the scene said the mosque was heavily damaged in the blasts, with holes left in the walls near the blast sites. The bombs went off within a minute of each other while the preacher was delivering his sermon and sparked a fire in a small library within the mosque, according to a local police official. Security forces sealed off the area following the attack.
The police official spoke on condition of anonymity because he was not authorized to speak to media.
Samarra, 95 kilometers (60 miles) north of the Iraqi capital, is largely Sunni Muslim and is home to a revered Shiite shrine.
There has been a spike in attacks on Sunni mosques in recent months.
Much of the violence tearing through Iraq is the work of the local branch of al-Qaida, a Sunni extremist group. While it is possible that Sunni insurgents could be to blame for the mosque attacks, hoping to stoke sectarian hatred, Shiite militias may also be behind the assaults.
Iraq's security forces and the government are dominated by Shiites. The sect's militias have been largely quiet in recent years, but they are now remobilizing as sectarian tensions rise in Iraq and as their loyalists travel to fight alongside government forces in neighboring Syria.
Last week, a similar attack on a Sunni mosque in northeast of Baghdad killed 33 worshippers.
Associated Press writer Sameer N. Yacoub contributed reporting.
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.