The towns blockaded by militants are al-Foua and Kefraya in Syria’s northwestern province of Idlib.
The government-held towns at the Lebanese border are Zabadani and Madaya, Reuters cited al-Manar TV station as reporting on Wednesday.
Zabadani is located about 47 kilometers (30 miles) northwest of Damascus and Madaya lies about 40 kilometers (25 miles) northwest of the capital.
The warring sides agreed a local ceasefire for the four towns in September, though the agreement has not been fully implemented.
The conflict in Syria, which flared in March 2011, has claimed the lives of some 470,000 people and left 1.9 million injured. Moreover, 6.36 million people have been displaced internally and more than four million others have fled the country since the beginning of the conflict.