Baghdad, Iraq ? A suicide bombing in the north and street battles hundreds of miles away in a Shiite holy city in the south claimed 16 lives Tuesday, demonstrating the tenuous security in Iraq as the U.S. focuses on curbing sectarian violence in Baghdad.

Nine people died in the suicide attack outside the regional party headquarters of Iraq’s president in the northern city of Mosul.

In Karbala, a Shiite holy city 270 miles south of Mosul, gunbattles broke out after police raided the office of Mahmoud al-Hassani, a Shiite cleric known for anti-American and anti-Iranian views. Police said they were searching for weapons.

Al-Hassani’s followers responded by attacking police stations and checkpoints in at least five areas of the city, residents and officials said. Gunmen in civilian clothing fired Kalashnikov rifles, machine guns and rocket-propelled grenades at Iraqi army patrols.

In Baghdad, meanwhile, the U.S. military said car bombs triggered deadly explosions Sunday in a Shiite neighborhood, backing away from assertions that the blasts were caused by an accidental gas leak.

The attack in Baghdad’s predominantly Shiite neighborhood of Zafraniyah was one of the deadliest in recent weeks, underscoring the security challenges facing U.S. forces as they attempt to quell the sectarian violence gripping the capital.

On Monday, U.S. Major Gen. William Caldwell told reporters that the U.S. explosive experts at the scene found “no evidence” of bombs or rockets, as police and witnesses described Sunday night. But senior Iraqi officials insisted that the blasts were related to the ongoing sectarian strife. On Tuesday, U.S. military corrected its conclusion.

In a statement Tuesday, the U.S. military said two vehicle bombs exploded near the apartment building, triggering a gas explosion in the nearby Hawra market.