Lebanese army and citizens gather at the site of an explosion, in the predominately Shia town of Hermel, about 10 miles from the Syrian border in northeast Lebanon, Saturday, Feb. 22, 2014. AP Images

A suicide bomber killed two Lebanese soldiers and a civilian with a car bomb at an army checkpoint in a Hezbollah stronghold in northeast Lebanon on Saturday, security sources said. The blast also wounded 17 people. It was the third such attack in recent weeks in Hermel, a predominantly Shia Muslim area near the border with Syria.

The Nusra Front in Lebanon – an armed Sunni group named after one of the factions fighting against President Bashar al-Assad in Syria – said it carried out the attack in a statement posted on Twitter and a website used by armed groups.

The Shia group Hezbollah, an Iranian-backed political and military movement, is fighting alongside Assad's forces against predominantly Sunni Muslim rebels in a conflict that has exacerbated sectarian tensions in Lebanon.

Assad is a member of the Alawite sect, an offshoot of Shia Islam.

The bombing followed a suicide attack in Beirut Wednesday that targeted an Iranian cultural center. An armed Sunni group, the Abdullah Azzam Brigades, said it had carried out that bombing, which killed eight people, as a reprisal for the military involvement of Hezbollah and majority Shia Iran in the Syrian war.

Security is one of the main challenges facing a new Lebanese government that took office a week ago, after the country went for nearly a year without a cabinet because of political tensions fuelled by the Syrian conflict.

Prime Minister Tammam Salam, the highest-ranking Sunni Muslim in the administration, condemned Saturday's attack as an act of “terrorism.”

“The attack on the military establishment exceeds a normal crime. We urge everybody to unite," he said.

Security forces cordoned off the area after the blast.

Hezbollah is a long-standing ally of Damascus. It says it is fighting in Syria to prevent Sunni radicalism from spreading to Lebanon. Its Lebanese critics say it must pull out and that Hezbollah's role in Syria is provoking such attacks.

Al Jazeera and wire services