The offensive is the third big assault on the self-proclaimed caliphate in recent days.
The offensive is the third big assault on the self-proclaimed caliphate in recent days after Iraqi forces attempted to storm Falluja in central Syria and a Syrian militia advanced with U.S. support towards Manbij in the north near the Turkish border.
The offensives are some of the most aggressive campaigns against Islamic State since it declared its aim to rule over all Muslims from parts of Iraq and Syria two years ago.
Friday's assault saw the army reach the edge of Syria's Raqqa province after heavy Russian air strikes hit Islamic State-held territory in eastern areas of neighbouring Hama province.
Raqqa city, further east, is Islamic State's de facto capital in Syria and, along with Mosul in Iraq, the ultimate target of those seeking to destroy the group.
State media said on Friday the army had made territorial gains and inflicted heavy casualties on the militants.
Syrian army spokesmen were not immediately available for comment.
State media has given no indication of how many troops are involved in the offensive, or what weaponry they might be using.
The Observatory also had no comment about numbers or weapons, but said at least 26 Islamic States militants had been killed along with nine from the Syrian and allied forces.
The war monitor said the army advance meant it was now almost 40 km from an area in which U.S. backed rebels were also waging an offensive to isolate the militants' strongholds in northern Aleppo from their territories east of the Euphrates river, where Raqqa city is located.
Should the army be able to reach the area where the rebels are also fighting Islamic State, that would leave the ultra hard line group hemmed in, albeit by forces highly unlikely to work together as they are on opposing sides in the multi-faceted conflict.
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