File Photo: A Syrian firefighter extinguishes a burned bus at the site of a deadly explosion, in Damascus, Syria. AP
The ministry said in a terse statement that the officers were returning to the capital Damascus from the southern province of Daraa. The bomb exploded on the north-south highway near the town of Khirbet Ghazaleh.
It said seven officers were seriously wounded.
Such attacks are not uncommon in Syria, where a nearly 12-year-old conflict has killed hundreds of thousands and displaced half the country's pre-war population of 23 million.
In October, a bus bombing killed 18 Syrian soldiers in a Damascus suburb and wounded at least 27 others.
Similar attacks over the years have killed and wounded dozens of soldiers in government-held parts of the war-torn country. In March last year, militants attacked a military bus near the historic town of Palmyra in central Syria, killing 13 troops and wounding 18 others.
Syrian authorities usually blame members of the Islamic State group who have been active in southern and central Syria, despite their formal defeat in Syria in 2019.
The leader of IS group, Abu al-Hassan al-Hashimi al-Qurayshi, was killed in battle with Syrian opposition fighters in Daraa province in mid-October.