MOSCOW/BEIRUT: President Vladimir Putin has signed a law ratifying a deal with the Syrian government allowing Russia to keep its air base in Syria for almost half a century, official documents show.

The original deal, signed in Damascus in January, sets out the terms under which Russia can use its Hmeimim air base in Latakia which it has used to carry out airstrikes against forces opposing President Bashar Assad.

Putin approved the agreement late Wednesday, after the two chambers of the Russian Parliament backed it earlier this month, according to the state’s official information portal.

The document says Russian forces will be deployed at the Hmeimim base for 49 years with the option of extending that arrangement for 25-year periods.

The base has been at the heart of Moscow’s military foray since it intervened in the conflict in September 2015, helping turn the tide in favor of Assad, one of Russia’s closest Middle East allies.

Separately, Syrian government forces neared Sukhneh, the last major town held by Daesh (ISIS) in Homs province, part of their multipronged advance toward militant group’s strongholds in the east of the country, a military source said Thursday.

The source said combat operations would accelerate toward the town, some 50 kilometers from the administrative frontier of Deir al-Zor province, where Daesh has redeployed many fighters after losing ground in Syria and Iraq.

“Capturing Sukhneh means opening the door and path for forces to move to Deir al-Zor directly,” the source told Reuters, adding that the military had captured positions 8 kilometers southwest of the town Wednesday evening.

Deir al-Zor province, which borders Iraq to the east, is almost entirely under Daesh control.

Daesh is losing ground fast in Syria to separate campaigns waged by the Russian-backed Syrian government on the one hand, and to U.S.-backed Kurdish forces and their allies on the other.

Government forces, backed by the Russian air force and Iran-backed militias, have also been advancing against Daesh in Hama province and in southern areas of Raqqa province. U.S.-led operations against Daesh are currently focused on taking Raqqa city, half of which they have captured.

The U.N. said Thursday that 20,000 people have fled their homes in the area of the group’s de facto capital since April 1.