Tension is simmering in Eastern Ghouta after news spread that more than 20 leaders of Tahrir al-Sham, an extremist alliance dominated by the former al-Nusra Front (ANF), had been executed by another armed group, an activist said.

Rival coalition Jaish al-Islam, which controls part of the region, has been engaged in violent battles with Tahrir al-Sham for months, and has succeeded in weakening the alliance's control in several areas.

"The security situation is very bad in all areas of Eastern Ghouta, especially the areas in which both Jaish al-Islam and Tahrir al-Sham have a presence," said activist Mohammed al-Beik of the Eastern Ghouta co-ordination committee.

News spread on Monday (December 18th) that Jaish al-Islam had executed a large number of Tahrir al-Sham emirs and leaders while they were detained in Jaish al-Islam's prisons.

Accounts varied, al-Beik told Diyaruna, but many sources agreed that 20 were killed in total, most of them foreigners.

Jaish al-Islam issued a statement Monday in which it denied having killed Tahrir al-Sham's leaders while they were detained, and said this falls "within the policy of lies and deception that al-Nusra Front practices".

The executions were revealed after the two sides reached an agreement that Jaish al-Islam would release Tahrir al-Sham elements it had detained during clashes in Eastern Ghouta from its prisons, al-Beik said.

Reports say the executions had taken place during battles between the two rival groups in al-Shaari area last April.

The released prisoners were to have rejoined a group of Tahrir al-Sham elements who were set to leave Eastern Ghouta for Idlib, pursuant to an agreement struck between the alliance and the Syrian regime, al-Beik said.

This called for Eastern Ghouta to be designated as a de-escalation zone in September.

Jaish al-Islam confirms executions

Jaish al-Islam responded to the list of detainees submitted by Tahrir al-Sham by confirming it did have some of the listed detainees, and admitted to executing others during the battles that took place in al-Shaari, al-Beik said.

Tahrir al-Sham considered this a breach of previous agreements that called for a stop to the executions, and Jaish al-Islam responded by saying the executions had occurred during the battles, not after.

When the names of the executed individuals were circulated, both groups went on maximum alert, al-Beik said, adding that residents fear the situation will escalate and the battles between the two sides will resume.

Both groups are headquartered in residential areas, he noted, "so any clash between the two sides would inevitably lead to civilian casualties".

The following list of names were confirmed to have been among those executed by sources with links to both sides, al-Beik said.

They include Syrian elements Abu Hafs al-Hufayri, Abu Hassan al-Shami, Abu Bakr al-Joulani and Abdel-Hamid al-Qaseer, also known as "Abu Jawhar".

Non-Syrians include Moaz al-Qafari, Al-Mulla Abu Bakr al-Urduni, Abu al-Zubayr al-Urduni, Mohamed al-Mheimidi, Abu Abdullah al-Qusaimi, Abu Maryam al-Urduni, Abu Hafs al-Urduni and Abu Maria al-Urduni.