International envoy Kofi Annan warned Thursday that Syria is drifting toward full-blown civil war and blamed the failure of his peace plan primarily on President Bashar al-Assad's government. He urged the divided UN Security Council to threaten "consequences" if Assad doesn't stop the violence.

Increasingly impatient with the Syrian regime, Annan confirmed for the first time that his six-point plan is not being implemented. He said it's now time for the UN's most powerful body and the wider international community to step up the pressure to ensure its implementation or start discussing other options to stop the bloodshed.

Annan spoke amid dire signs that diplomatic efforts to end the conflict are failing: UN observers came under fire Thursday as they tried to reach the site of the latest reported mass killing in Syria — about 80 people, including women and children who were shot or stabbed.

Adding to concern about the unarmed observers, UN Secretary-General Ban Ki-moon told the Security Council that UN patrols in Syria have been regularly obstructed and in some cases deliberately targeted, citing examples where a heavy weapon, armour-piercing ammunition, and a surveillance drone were used, a senior UN official said.

Annan, the joint UN-Arab League envoy, urged the Security Council to make clear that there will be "consequences" —usually code for sanctions — if his peace plan is not fully implemented.

"Clearly, the time has come to determine what more can be done to secure implementation of the plan," Annan said. "We must also chart a clearer course for a peaceful transition, if we are to help the government and opposition, as well as Syrian society, to help resolve the crisis."

In a sign of increasing global concern at the escalating Syrian conflict, Annan, Ban and Arab League Secretary-General Nabil ElAraby addressed an open meeting of the UN General Assembly in the morning and spent three hours behind closed doors with the Security Council in the afternoon discussing how to get the Syrian government to implement the Annan plan.

"It is up to the Security Council to take action now," ElAraby told reporters.The message from Arab nations is that the UN's most powerful body should impose nonmilitary sanctions against Syria, which has been suspended from the organization, he said.

The U.S. and its European allies have tried unsuccessfully for months to threaten sanctions against Syria as the death toll has risen. But Russia and China, Syria's main allies, vetoed two Security Council resolutions that threatened possible sanctions, and they indicated their continuing opposition in a joint statement after a summit in Beijing on Wednesday. The statement also opposed any outside military interference or forceful imposition of "regime change" in Syria.

Nonetheless, Britain's UN Ambassador Mark Lyall Grant said it was time to try to adopt a new UN resolution "with clear time lines for sanctions in the event of non-compliance."

Russia's UN Ambassador Vitaly Churkin told reporters that the Syrian government hasn't complied with all provisions in the Annan plan but there have been "encouraging developments" including an agreement to allow in humanitarian agencies. He accused the armed opposition of not only failing to comply with the Annan plan but declaring their intention not to do so, which he called "a very dangerous development."

'Contact group' possible

In another diplomatic move, Annan said preliminary discussions are taking place about establishing a "contact group" comprising countries that could influence both sides in the Syrian conflict to end the violence. The group would likely comprise world and regional powers, including Iran.

"If they could come together and look at the problems in a coldly realistic manner ... and say let's co-operate and suggest a roadmap for the Syrians to consider and work really to steer everybody in the same direction ... we may make progress," Annan said.

Annan said Iran is an important country and expressed hope it will be "part of the solution." U.S. Ambassador Susan Rice called Iran "part of the problem" because it is supports the government's campaign of violence and hasn't demonstrated it's ready "to contribute to the solution."

Russia's Foreign Minister Sergey Lavrov has proposed holding an international conference that would attract all countries that can influence Syria. Churkin, Russia's UN envoy, said the proposal "is very much in line" with Annan's idea of a contact group

Syria could face 'all-out civil war'

Annan said the international community had united behind his peace plan "but it now must take that unity to a new level" and "act as one."

Otherwise, he said, Syria will likely face a future of "brutal repression, massacres, sectarian violence, and even all-out civil war."

After months of acrimonious debate and finger-pointing, the Annan plan was the first international measure that won support from Russia and China as well as the U.S. and Europe. But in the West, there is growing dismay at its unraveling, and the potential for a spillover across the region.

In his briefing to the General Assembly, Annan said he told Assad nine days ago in Damascus that he wasn't implementing the peace plan and strongly urged him "to take bold and visible steps to now radically change his military posture."

Annan said Assad called militants the main obstacle, but he told diplomats that while all parties must cease violence, "the first responsibility lies with the government."

Since his visit, Annan said "shelling of cities has intensified, government-backed militia seem to have free rein with appalling consequences ... and president Assad has not indicated a change of course."

Syria's UN Ambassador Bashar Ja'afari insisted, however, that "the government of Syria has spared no efforts to implement its part of the Kofi Annan plan." He said an unjustifiable massacre is taking place in his country but insisted the government is not responsible.

The violence in Syria has grown increasingly chaotic in recent months, and it is difficult to assign blame for much of the bloodshed. The government restricts journalists from moving freely, making it nearly impossible to independently verify accounts from either side. The opposition blames government forces and militias that support them, known as shabihas, while the government blames rebels and "armed terrorist groups."

At the start of the General Assembly meeting, assembly president Nassir Abdulaziz Al-Nasser asked the 193-member world body to observe a minute of silence for Syrians killed in the latest massacres. Annan expressed "horror and condemnation" at the new massacre and demanded that the perpetrators be held accountable saying: "We cannot allow mass killing to become part of everyday reality in Syria."