Islamic State captured ground from Syrian government forces near the eastern city of Deir al-Zor on Monday, a group monitoring the war said, pressing a three-day assault which state media says has killed 300 people.
The Syrian Observatory for Human Rights said there was still no word on the fate of over 400 people it reported kidnapped when Islamic State – also known as Isis – began to attack government-held areas of the city on Saturday. State media has made no mention of the abductions.
Deir al-Zor is the main city in a province of the same name. The province links Islamic State's de facto capital in the Syrian city of Raqqa with territory controlled by the militant group in neighbouring Iraq.
Islamic State, in control of most of Deir al-Zor province, has laid siege since March to remaining government-held areas in the city of Deir al-Zor.
This was the third day of Isis attacks on the towns of Ayyash and Begayliya, which lie to the northwest of Deir al-Zor city on the approach from Raqqa.
Islamic State has now taken control of areas in the south and west of Begayliya, and has seized the Saeqa military camp near the town of Ayyash, the Observatory said.
A Syrian official source told Reuters the Syrian army repelled the attacks but Islamic State was continuing the offensive.
Speaking to Al Mayadeen television news early on Monday, Deir al-Zor’s governor said the security situation in Begayliya was “excellent”.
Syria's state news agency Sana said on Sunday that at least 300 people, including women and children, had been killed during the attacks in Deir al-Zor.
The observatory says about 400 people said to have been kidnapped had been taken to countryside to the west of the city, closer to Raqqa.
The United Nations has warned that about 200,000 besieged residents in Deir al-Zor faced severe food shortages and sharply deteriorating conditions.
The Syrian government has dropped some basic commodities into the city in recent weeks, and Russia said on Friday it had dropped 22 tonnes of aid to the besieged part of the city.
The Syrian foreign ministry said on Monday it had written to the United Nations condemning the attack. Lebanon's Hizbullah, which is fighting alongside President Bashar al-Assad's government in Syria, also condemned the attacks by Islamic State in a statement on Monday.