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 outburst of violence to hit the country.

Iraq is weathering its worst bout of attacks in half a decade. The violence has 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 US-led invasion.

The past several months have been the deadliest since 2008. More than 4,000 people have been killed since the start of April, according to UN figures.

Friday’s attack took place in the city of Samarra, where the deputy head of the municipal council said bombs were placed inside two of the mosque’s air-conditioning units. The explosions went off around midday, during Friday prayers. The official, Mizhar Fleih, said the explosion also wounded at least 21 people.

Fleih said that the Musaab Bin Omair mosque was heavily damaged in the attack.

“We are worried that the attacks on Sunni and Shiite mosques aim at reigniting the sectarian strife in this country, “he added.

Samarra, 95 kilometers (60 miles) north of the Iraqi capital, is largely Sunni Muslim and is home to a revered Shiite shrine.

There has also been a spike in attacks on Sunni mosques in recent months. While it is possible that Sunni extremists could be to blame, Shiite militias that had been largely quiet for years may also be behind those assaults.

Last week, a similar attack on a Sunni mosque in northeast of Baghdad killed 33 worshippers.

Copyright 2013 The Associated Press