IS, which controls large swaths of territory in both countries, is fighting Syrian troops, US-backed fighters and opposition militants in northern Syria and is facing an offensive by Iraqi forces on their stronghold of Fallujah.
The Syrian government has had no presence in Raqqa since August 2014, when IS captured the Tabqa air base and killed scores of government soldiers. The provincial capital, Raqqa, became the militants' first city.
The media arm of Lebanon's Hezbollah group, which is fighting alongside government forces, said Syrian troops reached the border of Raqqa province after advancing about six kilometers this afternoon. The front line is around 80 kilometers from the city of Raqqa.
Syrian troops began their advance toward the province Wednesday, the same day that US-backed forces launched an attack on the IS-stronghold of Manbij, some 115 kilometers to the northwest of Raqqa. It is unclear if the attacks were coordinated.
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The Observatory said SDF fighters had captured 34 villages near Manbij. Another activist group, the Local Coordination Committees, said the fighting is now concentrated on the south of the town.
IS fighters are also engaged in fierce battles for the rebel-held stronghold of Marea, a town some 70 kilometers west of Manbij. IS has surrounded Marea on three sides but has failed to capture the city, which is under control of rebels and fighters from the al-Qaida affiliated Nusra Front.
While battles rage in Raqqa province, Manbij and Marea, IS fighters are also coming under fire in their Iraqi stronghold of Fallujah. Iraqi forces launched their offensive on the city almost two weeks ago, and say they are on the edge of the town.
Violence in and around the contested northern city of Aleppo, Syria's largest and once commercial center, claimed more lives today. The city has been the scene of fierce fighting, even during a truce brokered by US and Russia that went into effect in late February and collapsed weeks later.