Jaafari accused rebels of obtaining material to produce chemical weapons "from outside powers -- mainly speaking, Turkey, Saudi Arabia and Qatar."
In a letter to the United Nations, Syria asked for the U.N. weapons inspectors to stay in the country beyond their weekend deadline, Jaafari said.
U.N. Secretary-General Ban Ki-moon did not address the letter directly but seemed to ask for a reprieve Wednesday for the sake of the inspectors. "The team needs time to do its job," he said from The Hague, where he visited the International Criminal Court.
He said the inspectors had already collected valuable evidence.
Russia, a close ally of Syria, is expected to use its veto power to block a resolution, setting up a possible diplomatic showdown.
Foreign Minister Sergey Lavrov insists there is no proof yet Syria's government is behind the chemical weapons attack.
The ministry accused Washington of trying to "create artificial groundless excuses for military intervention."
"The West handles the Islamic world the way a monkey handles a grenade," Russian Deputy Prime Minister Dmitry Rogozin tweeted.
China, which also has a permanent seat on the council, would also probably object to military measures.
"It's time that the United Nations Security Council shouldered its responsibilities on Syria, which for the past two and a half years it's failed to do," British Foreign Secretary William Hague said Wednesday.
He added that even if China and Russia veto a resolution, "We and other nations still have a responsibility" to act.
Iranian Foreign Minister Mohammad Javad Zarif, meanwhile, warned of "graver conditions" if strikes are carried out against Syria.
"If any country attacks another when it wants, that is like the Middle Ages," he said.
U.S. ruled out ground troops
For almost two years, Obama has avoided direct military involvement in Syria's bloody civil war as the death toll skyrocketed to more than 100,000, according to U.N. estimates.
But Obama had warned that a chemical attack would cross a "red line."
The White House previously ruled out sending ground troops to Syria or implementing a no-fly zone to blunt al-Assad's aerial superiority over rebels.
Brahimi said international law requires that that the Security Council approve military action.
"I do know that President Obama and the American administration are not known to be trigger-happy," he said. "What they will decide I don't know."
Outside of the United Nations, a military coalition is taking shape among Western powers.
France has also signaled it would join Western military intervention against forces supporting al-Assad.
President Francois Hollande said France is "ready to punish those who made the decision to gas these innocent people."
The French Parliament will hold a session next week to debate the situation in Syria.
German Chancellor Angela Merkel and British Prime Minister David Cameron spoke by telephone Wednesday about the crisis.