BEIRUT (AFP) - The Islamic State group seized territory from both Syrian government forces and rival rebels over the weekend further expanding the caliphate it has proclaimed straddling Iraq and Syria.

The Syrian Observatory for Human Rights said that following gains in both Homs province in the centre and Aleppo province in the north, IS now controlled half of the country's land area.

Geographer and analyst Fabrice Balanche said that across Iraq and Syria, the jihadist group now controlled nearly 300,000 square kilometers (115,000 square miles), an area the size of Italy.

In Aleppo province -- on Syria's border with Turkey -- IS has expanded its control at the expense of rival rebel groups.

IS captured the village of Suran on Sunday taking them to within 10 kilometers (six miles) of the border, the Observatory said.

Three days of heavy fighting left 30 IS fighters and 45 rival rebels dead, the Britain-based watchdog said.

On Monday, the group advanced towards the town of Marea, which lies on a key supply route from Turkey for its rebel opponents.

IS previously targeted Marea in April, detonating two car bombs and killing 15 rebel fighters, but it was unable to take the town.

In central Syria, IS ousted government forces on Saturday from a strategic crossroads south of the ancient oasis city of Palmyra.

The checkpoint and nearby village of Basireh lead south to Damascus and west to Homs, as well as east to IS-controlled areas of Iraq.