Fighting between Islamic State militants and the Syrian army was reported on Saturday near an ancient citadel in the historic city of Palmyra, the target of a big offensive by the jihadist group that has raised concern for the UN world heritage site.
The Syrian Observatory for Human Rights, a UK-based group that reports on the war, also said Islamic State militants had executed 23 people on Friday including nine minors and five women in areas seized from state control outside the city.
It marks the second mass execution reported since Islamic State advanced this week into the area some 240 km (150 miles) northeast of Damascus. In the first, the Observatory said the jihadists had executed 26 men, beheading 10 of them.
It reflects the pattern of attacks by the group elsewhere.
The Islamic State offensive in central Syria has added to the pressures facing government forces that have faced significant setbacks since late March in the four-year-long war.
Palmyra, also known as Tadmur, is home to extensive ruins of one of the most important cultural centers of the ancient world and was put on UNESCO's World Heritage danger list in 2013.
Islamic State, which espouses a puritanical Islamist ideology, has destroyed antiquities and ancient monuments in Iraq. The Syrian government's antiquities chief has said the jihadists will destroy Palmyra's ruins too if they take the area.
The Syrian military has been mounting air strikes against Islamic State fighters in the area. Rami Abdulrahman, who runs the Observatory, said the sides were fighting near a military intelligence building in Palmyra on Saturday.
Fighting was also reported at a gas field to the east of Palmyra. A statement posted by Islamic State supporters on Twitter said the group had taken large parts of the gas field.
Other insurgent groups fighting President Bashar al-Assad have seized control of wide areas of the northwestern province of Idlib since late March. Assad has also lost a border crossing with Jordan in the south.
This week the Syrian army and the allied Lebanese group Hezbollah have driven insurgents from wide areas of the mountainous region to the north of Damascus, shoring up Assad's grip over the border zone between Syria and Lebanon.
