A bomb attack targeting a weapons bazaar in eastern Syria close to the Iraqi border has killed 30 "terrorists", according to Syrian state TV.
"A big explosion hits a terrorist arms market in Mayadeen, killing 30 terrorists and wounding dozens of others," the television reported.
Just 80km from the Iraqi border, the town is under the control of rebel groups, including Al-Qaeda's Syria affiliate the Al-Nusra Front.
Al-Nusra has been fighting the jihadist Islamic State of Iraq and Syria.
ISIS is the same cross-border group which has spearheaded an offensive in neighbouring Iraq this week that has seen militants sweep down from second city Mosul towards Baghdad.
A rebel spokesman from Deir Ezzor province contested the television's report, and told AFP the blast was a car bomb planted by ISIS that killed at least 15 civilians in a street market.
"Light weapons are sold nearby, but the targeted area was a street market and those killed were civilians," spokesman Omar Abu Leyla said.
ISIS's fighters in Syria have been under attack by rival rebels since the start of the year.
They have been driven out of much of northwestern Syria, but retain control of the city of Raqa up the Euphrates Valley from Deir Ezzor.
They have tried repeatedly to extend their area of control to the Iraqi border to unite their forces in the two countries.
Elsewhere, A Muslim cleric of Chechen origin who was arrested in Austria this month has denied allegations that he recruited young Muslim men to fight in Syria.
Authorities in Graz took the suspect, 41, into custody after raiding buildings belonging to the city's Taqwa Islamic community.
The man, whose name has not been disclosed, is suspected of radicalising and encouraging several young Chechen refugees to join the uprising against Syrian President Bashar al-Assad.
The authorities say four of them had died in combat.
His arrest is one of several in Europe in recent months amid fears that radical fighters returning from Syria could stage attacks on European soil.
The man told Profil magazine he was innocent and that he had in fact warned Chechens against joining the war in Syria.