At least three people were killed Friday when Syrian forces shelled restive areas near the Turkish-Syrian border and the outskirts of Damascus, activists said.
"The shelling of Jabal al-Zawya in the northern province of Idlib has killed two people, while another person was killed in the area of Doumeir, near Damascus," activist Haytham al-Abdullah told dpa.
The chief of the UN military observer mission supervising the fragile ceasefire said the army must make the first move to stop the violence.
"The strongest party needs to make the first move," Major General Robert Mood was quoted as saying.
Mood, who on Thursday toured the restive cities of Hama and Homs, said that starting Friday there would be eight UN observers in the southern province of Daraa, 12 in Homs, eight in Hama and four in the north-western province of Idlib.
An advance team of unarmed UN observers arrived in Syria on April 16 to supervise a UN-brokered ceasefire, but up to 300 monitors are due to arrive over the coming weeks.
The peace plan of international envoy Kofi Annan calls for a halt to fighting, the withdrawal of heavy weapons from urban areas, a daily humanitarian ceasefire, media access and political dialogue between the two rival sides.