AMMAN/BEIRUT (Reuters) - The Syrian army and Islamic State militants waged fierce battles on Wednesday around Khanaser, a strategic town southeast of Aleppo, where an attack by the jihadist group has cut the main land route to the city during three days of fighting.
A government military source denied reports Khanaser had fallen to Islamic State. But he said its fighters were firing on it from nearby positions.
"They are around Khanaser - it is under their sniper fire," the source told Reuters.
Islamic State is escalating its assaults on government-held areas. Its suicide bombers launched some of their deadliest attacks of the war on Sunday in Damascus and Homs, killing about 200 people. It also attacked government forces near Palmyra on Wednesday.
The attacks appear to be a preemptive move, the military source said, because the militants expect to come under more pressure from the Syrian army soon. The group is not part of a U.S.-Russian plan to halt fighting in Syria, due to start on Saturday.
Suicide bombers also helped Islamic State seize Khanaser, according to Amaq, a news outlet that supports the group. It said three of them drove into army fortifications there - a tactic the militants have used before to take government-held towns.
Two rebel sources credited the Islamic State attack with relieving pressure on them around Aleppo.
The latest attack cut a main army supply route to parts of Aleppo where the Syrian army, backed by Russian warplanes, Iran's Revolutionary Guards and Lebanon's Hezbollah, has been gaining ground. Islamic State also said it hit an army convoy between Salamiya and Athriya that was heading to Khanaser.
The military source said the road was closed as a result of military operations, denying Islamic State had seized it.
"There were fierce battles yesterday evening, in which Daesh suffered large numbers of dead, and three armored vehicle bombs were destroyed," the source said, using the Arabic acronym for Islamic State.
Russian air strikes hit Islamic State outposts near Khanaser while army artillery pounded them from government-held Safira, a rebel source said.
Separately, the army said it had repelled infiltration by Islamic State militants against the government-held towns of al Barda and al Bayarat almost 10 km (six miles) west of Palmyra and killed dozens of militants. The militants seized the ancient city of Palmyra from the government in May.
The Syrian army and its allies have also extended their control of parts of a road running towards the jihadist group's stronghold of Raqqa, building on gains made earlier this month.
(Reporting by Suleiman Al-Khalidi and Tom Perry, editing by Larry King)