Islamic State (IS) fighters have reportedly captured the Syrian town of Maheen, in central Homs Province, from government forces.
They launched the offensive with two suicide car blasts late on Saturday, the UK-based Syrian Observatory for Human Rights says.
Clashes were also taking place in nearby Sadad, a mostly-Christian town.
The latest development comes amid air campaigns in Syria by Russia and a US-led coalition.
Islamic State has been expanding from its mainly northern and eastern strongholds towards Homs in central Syria in recent months. The group overran the town of Tadmur - home to the ancient ruins of Palmyra - in May, and later took al-Qaryatain town in August.
The latest offensive on Maheen and Sadad brings IS to within 20km (13 miles) of the main road that links the Syrian capital Damascus to Homs and other cities further north.
The Observatory said at least 50 government soldiers were killed or wounded in the fighting. The attack on Maheen began late on Saturday with twin suicide car bombs, a favoured tactic for IS militants launching an assault.
By Sunday morning the Observatory reported that the whole town was reported to be in IS hands. An IS statement also said the group had taken the town.
Maheen is home to a large military complex and arms depot.
Meanwhile, clashes between government troops and IS are said to be continuing on the outskirts of Sadad. The town is home to Syria's Assyrian Christian minority, where the ancient language of Aramaic is still spoken.
It comes amid continued Russian air strikes in support of Syrian President Bashar al-Assad, which Russian officials say are targeting IS and other "terrorist groups".
However, activists on the ground say the strikes have been hitting moderate rebels and civilians in western areas, where IS have little or no presence.
They said more than 60 people were killed by Syrian army raids and Russian strikes in the northern province of Aleppo on Saturday. On Friday, more than 70 people were reported killed and hundreds more wounded in an air strike and shelling on a market in the rebel-held Damascus suburb of Douma.