A bomb attack targeting a weapons bazaar in eastern Syria close to the Iraqi border killed 30 "terrorists" on Saturday, state television reported.
"A big explosion hits a terrorist arms market in Mayadeen, killing 30 terrorists and wounding dozens of others," the television reported.
Just 80 kilometres (50 miles) from the Iraqi border, the town is under the control of rebel groups, including Al-Qaeda's Syria affiliate the Al-Nusra Front, that have been fighting the jihadist Islamic State of Iraq and the Levant.
ISIL 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 ISIL 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.
ISIL'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.