Al-Assad's government faults "terrorists," the term it uses to describe the opposition and rationalize security forces' crackdown.

But two groups part of that effort -- the Syrian National Council and the National Coordination Committee for Democratic Change -- blamed the regime. Opposition members have accused al-Assad's forces of high-profile bombings in the large cities of Aleppo and Damascus in recent months to undermine the resistance's credibility.

"This is a government-planned attack," said Ausama Monajed, the adviser to the Council's president. "We are in touch with the armed resistance."

Brig. Gen. Moustafa el-Sheikh, head of the rebel Free Syrian Army's military council, said that "no other parties in Syria ... are technically capable of making such a huge explosion, except for the regime itself."

"Not even al Qaeda can do that," he said.

Analysts said the attack raises concerns about the presence of jihadist elements in Syria, noting the Damascus strike resembles suicide car bombings during the sectarian civil warfare prevalent in the last decade in Iraq.

Bill Roggio, an analyst on terror and military issues, said he believes the attack "very likely" was carried out by an al Qaeda-linked militant group called the Al Nusrah Front for the People of the Levant, which has claimed credit for recent suicide attacks in Damascus and Aleppo.

He said another jihadi group called the Al Baraa Ibn Malik Martyrdom Brigade also has surfaced, and that al Qaeda in Iraq has had a "strong presence" in Syria. Foreign fighters entered Iraq through Syria during the war there.

Jeffrey White, a defense fellow and analyst at the Washington Institute for Near East Policy, concurred that Thursday's suicide strike is "coordinated (and) very destructive," much like what al Qaeda elements in Iraq claimed credit for.

While Roggio, the managing editor of the Long War Journal blog, called it "very concerning" that opposition groups have "ignored" or denied the activities of terrorist groups, White said opposition members aren't necessarily ignoring an uptick in terrorist activity.