At least 15 people have been killed and 50 others injured in a car bombing at an army checkpoint in a suburb of the Syrian capital Damascus.

Monday's explosion struck the town of al-Diyabiyah, which serves as one of the gateways for the many foreign pilgrims who visit Sayeda Zainab shrine, a Shia holy site located south of Damascus.

No one claimed responsibility for the attack.

One of the guards manning the checkpoint told AFP news agency that his bomb detector began beeping when a suspicious truck pulled up.

"We stopped the car at the checkpoint and when we began a manual search, they detonated the bomb," he said.

"My colleagues were killed."

Windows of a small hotel across the checkpoint were shattered by the force of the blast.

The hotel is occupied mostly by displaced Syrians from Fouaa and Kefraya, two Shia-majority towns in the northwest that are under siege by armed rebels.

The holy site, believed to contains the grave of Zeinab, a venerated granddaughter of Prophet Muhammad, is heavily guarded by the government forces.

The area around the shrine has been hit by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group several times this year.

In February, several ISIL bombings near the shrine left at least 134 people dead, most of them civilians, according to the Syrian Observatory for Human Rights.

READ MORE: More than 400,000 people killed in Syria since 2011

Shia fighters from Lebanon, Iraq and Iran claim to be fighting alongside Syrian President Bashar al-Assad's forces to defend the shrine.

Staffan de Mistura, the UN special envoy for Syria, has estimated that 400,000 people have been killed throughout the past five years of civil war.

More American troops

The car bombing near Damascus occurred on a day US President Barack Obama announced plans to send 250 more soldiers to Syria.

"I've decided to increase US support for local forces fighting ISIL in Syria ... I've approved the deployment of up to 250 US personnel in Syria, including special forces," Obama said.

He announced the decision after a meeting in Hanover with German Chancellor Angela Merkel.

The deployment, which will increase the number of American troops in Syria to about 300, aims to accelerate the process of driving back ISIL, according to Ben Rhodes, White House adviser.