The Islamic State of Iraq and the Levant has captured Syria’s ancient city of Palmyra, giving them control of almost half of the country, according to a monitoring group.

Located in central Homs province and in the heart of Syria, Palmyra lies 210km northeast of Damascus in desert that stretches to the Iraqi frontier to the east.

The UK-based Syrian Observatory for Human Rights said on Thursday that ISIL now controls approximately 95,000 sq km of land in nine out of 14 provinces since they declared their alleged caliphate – which puts them in control of almost half of the country.

The Syrian government previously lost the town of Bosra in Deraa province to ISIL in March, which had also been declared by UNESCO as a World Heritage Site.

In April, ISIL managed to capture and control most of Yarmouk, which is 8km away from the centre of Damascus. Yarmouk is mostly inhabited by Palestinian refugees.

Activists in Palmyra, who requested anonymity, told Al Jazeera that ISIL took full control of the city on Wednesday evening and people were trying to escape, with many left stranded on the streets.

“ISIL have infiltrated the city overnight. Power is down and we barely have any electricity or water. There is fear among residents and we do not know what to expect next,” one activist said.

“The Syrian regime has bombed several targets for ISIL since last night, but air strikes also targeted two mosques in the city – Othman Bin Affan and al-Iman mosques. Several people have been killed and others injured.

“Hospitals and clinics are being bombed too. There are not enough medical supplies or doctors to treat the injured.”

Activists and journalists working at the Palmyra Media Centre made it clear to Al Jazeera that they were incapable of leaving their homes.

Nasser, a journalist in Palmyra, told Al Jazeera that residents in the city could not leave and government forces offered no way out.

“There are almost 170,000 people here, including 50,000 internally displaced people from Homs and Der Ezzor,” he said.

“ISIL is hated by residents here and labelled terrorists. ISIL will not treat us any different than those elsewhere in areas they control. This is a new siege.”