No one has claimed responsibility for the suicide attack, but state television pinned the blame on terrorists, saying the car bomb was rigged with 1,000 kilograms of explosives.
State television broadcast footage of damaged buildings, smoldering cars, and trucks turned upside down. It also showed members of a United Nations-Arab League observer team visiting the scene of the blast.
The opposition Syrian National Council and the government accused each other of being responsible for Saturday's blast, as well as the twin bombings in Damascus on May 10.
But a spokesman for the rebel Free Syrian Army, Omar Abu Layla, denied any responsibility. He told Radio Sawa that his group could “not physically have reached the site because of “government security measures.” Another rebel commander told al Jazeera TV that the blast was a “pretext for the government in intervene in Deir al Zour.”
In Damascus Saturday, United Nations Under-Secretary-General for Peacekeeping Herve Ladsous, defended the agency's efforts to enforce the cease-fire.
“I would remind you that this is a process. We have reached certain elements of our objectives. We are not there yet, but it is a process that will be continuing with the support of all those concerned in order, first and for most, to achieve this cessation and, in the first time, confirm the reduction of the violence.”
There are now more than 200 unarmed U.N. peacekeepers in Syria, a number that should reach 300 by the end of the month.
Tensions between the government of Syrian President Bashar al-Assad and opposition groups remain high.
Activists accused Syrian forces of using tear gas and live ammunition on protesters in Aleppo, on Friday, in what opposition groups called one of the biggest protests since the anti-government uprising began 15 months ago.
Hopes for peace may get some boost from international envoy Kofi Annan. A spokesman says the former U.N. chief is planning to return to Damascus to again pursue a peaceful solution to the conflict.
The United Nations says the death toll from violence related to the anti-government uprising that erupted more than a year ago may now have reached 10,000.