BEIRUT (Reuters) - The Syrian army and allied forces have captured one of the last major Islamic State enclaves in the central Syrian desert, a monitor and a Hezbollah military media unit said on Saturday.

The pocket of territory totals around 2,000 square km (770 square miles), said the media unit run by Hezbollah, which fights alongside Syrian government forces in the war.

Earlier this week, the army and its allies encircled the IS militants after advancing southward to join up with their forces near al-Sukhna town in Homs province. The enclave extends from the west of al-Sukhna into nearby Hama province.

The Syrian army -- supported by Russian air power and Iran-backed militias -- secured al-Sukhna this month. It was the last major town in Homs province that Islamic State held.

The Syrian Observatory for Human rights, a Britain-based war monitor, said the army has seized dozens of hills and positions in that region in central Syria.

Now, the only significant Islamic State presence remaining in Homs was another nearby enclave on the provincial border with Hama, also under siege by the army and its allies, the monitoring group said.

Over the past year, Islamic State has lost ground to various separate enemies including Syrian government forces with their allies, and U.S.-backed militias.

IS militants still control most of Deir al-Zor province, which borders Iraq.