Governor of Homs province, where city is located, says army has sent reinforcements and is bombing fighters from air.
Nearly 300 people have been killed after several days of fighting between the Islamic State of Iraq and the Levant (ISIL) group and the Syrian government in the historic town of Palmyra, activists said.
The UK-based Syrian Observatory for Human Rights said on Sunday the dead included 123 Syrian government soldiers and allied militiamen, 115 ISIL fighters, and 57 civilians.
Reports of the deaths came as the Syrian government claimed it had repelled ISIL fighters from the ancient city, where the armed group had seized the northern part of the modern settlement, Tadmur.
Provincial governor Talal Barazi told the AFP news agency that the army had recaptured districts of the town which ISIL had overrun on Saturday.
Barazi said the army was “still combing the streets for bombs”, but that “the situation in the city and its outskirts is good”.
The ISIL advance on Palmyra had sparked international concern for the safety of the UNESCO World Heritage site. Syrian officials expressed relief that the armed group had been pushed back.
“We have good news today, we feel much better,” said antiquities chief Mamoun Abdulkarim.
“There was no damage to the ruins, but this does not mean we should not be afraid.”
ISIL launched a lightning offensive across the desert last week from their stronghold in the Euphrates Valley to the east, triggering ferocious fighting with the army, which has a major base just outside the oasis town.