At least 42 people have been killed in Syria's Eastern Ghouta as regime forces continue to launch air raids on the opposition-held enclave while edging closer to its central towns.

Activists in Douma, one of the main urban centers, told Al Jazeera on Sunday that Syrian jets have "not stopped bombing towns all over Ghouta".

Syrian regime television reported the town of Mudeira had been seized on Sunday by the army, which was now able to link up with units on the other side of Eastern Ghouta.

Regime forces have now surrounded Douma after capturing the neighboring town of Mesraba, 10km east of Damascus, on Saturday, it said.

The advance on Mudeira has driven a wedge deep inside the opposition-held territory, leaving Douma and Harasta cut off.

Civilians trapped

The UN estimates there are 400,000 civilians trapped in Eastern Ghouta.

Activist Nour Adam said eight people died in Jobar, a town east of the capital Damascus, and 16 people from the same family were killed in an attack on Douma.

The rest died in attacks that hit the towns of Harasta, Zamalka, and Irbin, Adam said.

On Saturday, the Syrian Observatory for Human Rights, a UK-based war monitor, told Al Jazeera that Eastern Ghouta had been divided into three - Douma and its surroundings; Harasta in the west; and the rest of the towns further south.

The regime's latest offensive on Eastern Ghouta, which began on February 18, has killed 1,099 civilians over the past 21 days, the Syrian Observatory reported.

The figure includes 227 children and 145 women, while at least 4,378 others have been wounded.

The Syrian Civil Defense, a volunteer rescue group also known as the White Helmets, said on Sunday a regime attack on Irbin a day earlier involved "chlorine ... phosphorus". It was the second alleged chemical attack to hit the suburb in a matter of days.

Previous pattern

The Syrian regime's offensive follows a pattern of previous assaults on opposition strongholds, deploying massive air power and tight sieges to force opposition fighters to accept "evacuation" deals.

These involve opposition surrendering territory in exchange for safe passage to opposition areas in northwest Syria, along with their families and other civilians who do not want to come back under Assad's rule.

Al Jazeera's Alan Fisher, reporting from Gaziantep along the border in neighboring Turkey, said Russian-backed Syrian forces tend to use military gains to try and secure a "political advantage".

"[They do so] by saying to fighters maybe you should move to another part of Syria," Fisher said.

On Friday, a number of opposition fighters and their families were evacuated from Eastern Ghouta, state media reported.

Wael Olwan, spokesman of the opposition group Failaq al-Rahman, with ties to the Free Syrian Army, denied on Sunday that such negotiations were taking place - despite the regime’s claims that talks with opposition groups were under way.

Suffocating siege
The Damascus suburb of Eastern Ghouta has been under the control of armed opposition groups since 2013 - two years after a popular uprising called for the removal of Bashar al-Assad.

The area has been under a suffocating siege by regime forces since then in an attempt to drive out opposition.

The ongoing fighting on multiple fronts, coupled with continuous shelling and air raids, has prevented desperately needed food and medical supplies from being delivered to residents trapped inside.

PHOTO CAPTION

Eastern Ghouta, The Damascus suburb, home to some 400,000 people [File: Anadolu]

Al-Jazeera