Syria's government wants to destroy the UN-brokered peace plan aimed at ending 14 months of civil conflict, opposition leader Burhan Ghalioun told reporters in Tokyo on Friday.
"The regime is now trying to kill this (Kofi) Annan plan, and by a new technique which is terrorism," Ghalioun said, a day after suicide bombers killed at least 55 people in horrific attacks in the capital Damascus.
Condemnation came from around the world after the deadliest blasts since the uprising began, with President Bashar al-Assad's embattled regime and the opposition trading accusations of responsibility for the carnage.
Ghalioun was adamant Friday that Assad's government was behind the attacks, which also wounded nearly 400 people, and accused the authorities of colluding with outside bodies.
"The regime has operated very closely with Al-Qaeda," he told reporters, adding that the bombings marked a change in tactics.
"We have to notice the timing of these bombings, the bombings started almost as soon as the regime removed heavy forces from the cities, we think there is a connection," he said.
The blasts during the morning rush hour further clouded a UN-backed ceasefire brokered by special envoy Annan that has failed to take hold since it went into effect on April 12.
Russia and China, which have stymied Western efforts to heap stronger condemnation on Assad's government, joined a UN Security Council denunciation of the attacks.
The 15 Security Council members "condemned in the strongest terms the terrorist attacks" in the Syrian capital, according to a statement.
The council called on all sides to "immediately and comprehensively" implement the six-point peace plan of UN-Arab League envoy Annan, "in particular to cease all armed violence".
The explosions took place on a main freeway in the south of Damascus, in front of a nine-storey security complex whose facade was heavily damaged while nearby residential buildings collapsed.
"Is that the freedom you want? Students from schools and employees going to work are dead," shouted one man in the middle of the destruction.
Signup to our newsletter and follow us on Facebook and Twitter!
Syria's interior ministry said the suicide attackers used a tonne of explosives, killing at least 55 people and wounding 372.
It added that emergency workers filled 15 bags with body parts, and that the blasts also destroyed around 200 cars.
Washington called the Damascus attacks "reprehensible" while Annan described them as "abhorrent". Russia and China separately called for a halt to the violence and urged all parties in Syria to cooperate with Annan's peace plan.
Ghalioun, the president of the Syrian National Council, said the Annan plan was toothless and too easy to ignore.
"If the regime fails to implement the plan, it will not get punished, and that is our concern.
"Assad feels that he can run away from the plan without any consequences."
"The Annan plan is in crisis today," said Ghalioun. "If the Syrian regime continues challenging it, if it continues using terrorism and bombing, it will be killed.
"If the international community wants to save the Annan plan, they should start now. Those who try to kill the plan should be held accountable."
Ghalioun is in Tokyo to drum up support for his opposition movement amid continued diplomatic deadlock.
Assad's traditional allies, Russia and China, continue to block substantial moves by the international community to pressure the regime.
Ghalioun said a resolution of the situation in Syria was in the interests of the wider region.
"I believe it's clear the Syrian crisis is not only about Syria, or exclusively a Syrian crisis," he said.
"It has many regional and international dimensions. I believe if the Annan plan fails, so this chaos and disorder might spread outside Syria into countries that are very fragile but stable, that would include Lebanon (and) Iran."