BEIRUT (AP) — Russian military police deployed north of the central city of Homs on Friday, setting up checkpoints and observation points as part of a cease-fire in a third safe zone in war-torn Syria, but opposition activists said the truce was violated by government forces.

The truce that began Thursday and the deployment are part of the third of four planned cease-fires reached in recent months under an agreement brokered by Russia, Iran and Turkey in May that aims to "de-escalate" the violent Syrian civil war, now in its sixth year.

Russia and Iran are providing military support to President Bashar Assad, while Turkey sponsors some of the opposition forces arrayed against him.

The deployment came hours after government forces shelled the central town of Talbiseh just before midnight Thursday killing one person and wounding several others, according to the Britain-based Syrian Observatory for Human Rights and activist Mohammed al-Homsi who is based in Homs province.

Al-Homsi said that the shelling also targeted the nearby villages of Teir Maaleh and Gharnata. The Observatory and al-Homsi said the situation was calm Friday as Russian troops began deploying in the region.

The Observatory said dozens of Russian troops deployed on front lines between government forces and opposition fighters.

Russian Defense Ministry spokesman Igor Konashenkov announced the military police deployment on Thursday, saying the Russian military police will establish two checkpoints in the Harb Nafseh and Dayr districts and three observation posts in the districts of Khmeirat, Qubeibat and Tel Ameri.

Russian military police from the de-escalation monitoring forces will have to "ensure the disengagement of the opposing sides, monitor compliance with the cessation of hostilities and also ensure unhindered deliveries of humanitarian supplies and evacuations of those ill and injured," Konashenkov said.

Earlier on Friday, an explosion targeted an office of the al-Qaida affiliate in northern Syria, inflicting casualties.

The Observatory said the explosion occurred near the office belonging to the al-Qaida-linked Levant Liberation Committee adding that two of the militant group's fighters were killed and several others were wounded.

The Ibaa news agency, which is linked to al-Qaida, says the blast in the village of Urum al-Kubra, west of the northern city of Aleppo, left "several martyrs" and wounded people.

The explosion comes amid rising tension in northern Syria between the al-Qaida-linked group and other factions, including more moderate rebels.

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Associated Press writers Vladimir Isachenkov in Moscow and Albert Aji in Damascus, Syria contributed to this report.