BEIRUT (Reuters) - The Syrian army and allied militias launched an offensive in the Golan Heights on Thursday, in what rebels said was part of a major assault to regain ground in southern Syria the government had lost over the last three years.

Smoke rises following explosions in Syria near the border with the Israeli occupied Golan Heights September 23, 2014. REUTERS/Baz Ratner

Rebels said the attacks began at dawn, when the army stormed the village of Samdaniya al Gharbiya, near the border with Israel. The army said the village was captured, but rebels in the area said heavy fighting continued.

Under cover of rain and fog, government troops pushed towards the strategic town of Hamdanieh, in the Syrian Golan Heights, which they lost two years ago, according to residents and rebels.

“They staged a large-scale attack under cover of heavy fog, where you can hardly someone only a few metres away from you, on the two villages,” said Abu Yahya, a spokesman for al-Wiyat al Furqan, a rebel group in the area.

The attacks came in Quneitra province, a sensitive piece of territory around 70 km (40 miles) southwest of the capital, Damascus. It has seen frequent fighting between various insurgent groups and the Syrian military and its militia allies.

The army was mostly relying on ground troops and heavy artillery bombardments, said a member of another rebel group, Seif al Sham. Proximity to the Israeli border makes it difficult to use air power extensively.

Israel seized part of the Golan Heights from Syria in the 1967 Arab-Israeli war and annexed it later. Concern is growing in Israel over the presence in Quneitra of the Lebanese militant group Hezbollah, an ally of the Syrian government.

Syrian state media said Samir Qantar, a Hezbollah leader killed in Damascus two weeks ago, had been involved in another offensive earlier this year in Quneitra. Israel welcomed Qantar’s death but has not confirmed it carried out the attack that killed him.

The offensive in Quneitra was the government’s first in the south since Russia joined the war on Sept. 30 in support of its ally, Syrian President Bashar al-Assad. Thursday’s attacks came just days after an assault on the town of Sheikh Maksin that saw Russia’s heaviest bombing campaign so far in the south.

The commander of one rebel group in the region said Russia had launched at least 100 air raids against its positions over two days. The air campaign had tipped the balance in favour of the government, the commander said. But its initial gains were lost and the army repelled.

Before it gained Russia’s help, the government had mounted an offensive in the south last February but failed to make much headway after months of attacks.

Sheikh Maskin appears to be the main objective of the latest offensive. The town lies on one of the main supply routes from Damascus to the city of Deraa, close to the border with Jordan. Taking Sheikh Maskin would allow the army to press further south against other mainly rebel-held towns.

Rebels have seized almost 70 percent of the countryside over three years. But this year they failed to capture Baath city and Khan Arnabah, the last remaining major towns in hands of the government.

Baath city, effectively the provincial capital of Quneitra province, was shelled with mortars on Thursday in response to the army assault, two rebels in the area said.

(This story has been refiled to fix name of spokesman in fourth paragraph.)