At least seven Lebanese Shi'ite pilgrims were killed Sunday in Damascus when a bomb exploded on the bus carrying them to holy sites in the Syrian capital.
Authorities said another 20 pilgrims were wounded in the attack in the center of Damascus, near the shrine of Sayidna Ruqqaya.
Syria's state news agency SANA said the "terrorist bombing" involved five kilograms of explosives placed near the front of the bus and that a second device found on the floor of the bus had been defused.
Syria's al-Qaida affiliate, the Nusra Front, claimed responsibility for the attack, which gutted the bus and left pools of blood from the victims on the ground.
The Nusra Front accused the bus passengers of being Hezbollah fighters.
A tour bus operator in Lebanon said that Shi'ite pilgrims had been making weekly, daylong trips to the shrines throughout the nearly four-year-old Syrian conflict that has left about 200,000 people dead.
Drive out insurgents
Meanwhile, Syria's Prime Minister Wael al-Halqi told parliament on Sunday the country wanted to drive all insurgents out of its territory in 2015 and was prepared to back any attempts to fight global militancy.
Halqi said Syria's main aim was to "flush out all terrorists from its land" this year and it would "back any initiatives to fight global terrorism," a broadcast on state television showed.
He said Syria would not allow its enemies "to destroy the land of religions and cradle of civilizations" and praised the army for its efforts.
Syria has repeatedly said it wants to coordinate with other countries to fight armed groups in its country. It describes all anti-government forces in Syria as terrorists, unlike Western countries and their Arab allies who distinguish between the hardline jihadists and more mainstream rebel fighters.
Syria's uprising started in 2011 with anti-government protests and has descended into a civil war pitting a range of armed groups against the military. Hardline groups such as Islamic State and al-Qaida's Nusra Front have gained ground.
U.S-led forces started an airstrike campaign against the Islamic State group in Syria and Iraq last year when the militant group captured tracts of land in both countries.
President Bashar al-Assad said in a magazine interview published last week that U.S.-led airstrikes should be subject to an agreement with Damascus and Syrian troops should be involved on the ground.
Washington supports opposition forces fighting for the past four years to topple Assad, but its position has become complicated since Islamic State militants and other hardline groups emerged as the most powerful insurgent factions.
But it has rejected the idea of allying itself with the Syrian government despite them now having a common enemy.
Some material for this report came from Reuters.