The two towns lie to the east of the north-south highway running through Syria`s major cities that is crucial to control of mainly government-held territory in the west of the country. They are also close to roads that link the Islamic State-held city of Palmyra in the central Syrian desert to western cities.
The Observatory, which tracks Syria`s nearly five-year-old conflict using sources on the ground, said Syrian and Russian aircraft had carried out dozens of strikes on the areas surrounding Mheen and Hawwarin.
Russia, a main ally of President Bashar al-Assad, started carrying out air strikes in Syria nearly two months ago in support of the Syrian army and allied ground forces.
The West has accused Moscow of mainly targeting rebels unaligned with Islamic State during the campaign which started on Sept 30. Last week Russian and Syrian aircraft bombarded Islamic State-held areas of eastern Syria.
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