EMILY BOURKE: The Obama administration is warning of a dangerous escalation in the conflict in Syria after Russia's decision to send more attack helicopters to Damascus.
Both sides of the conflict are continuing to ignore the April ceasefire and now a senior UN (United Nations) official says the hostilities have become a full scale civil war with the Assad regime trying to retake large areas of cities lost to opposition groups.
Brendan Trembath reports from Washington.
BRENDAN TREMBATH: The conflict in Syria could be entering an even deadlier phase if the US secretary of state has the right information.
HILLARY CLINTON: We are concerned about the latest information we have that there are attack helicopters on the way from Russia to Syria which will escalate the conflict quite dramatically.
BRENDAN TREMBATH: Hillary Clinton revealed Russia's plan during a discussion at a Washington think tank.
The US has been pushing Russia for months to break its military ties with Syria.
HILLARY CLINTON: We have confronted the Russians about stopping their continued arms shipments to Syria. They have, from time to time, said that we shouldn't worry. Everything they are shipping is unrelated to their actions internally, that's patently untrue.
BRENDAN TREMBATH: Russia and Syria are old allies. Syria is home to a Russian naval base.
Russian attack helicopters would be a devastating new blow against opposition forces.
A senior UN official says the conflict is now a civil war.
The UN peacekeeping chief, Herve Ladsous, has told reporters that clearly the government of Syria has lost some large chunks of territory to the opposition and wants to retake control.
He says there's been a massive increase in violence.
Diplomatic hopes to resolve the crisis depend on whether or not the US and Russia agree on a plan for Syria's regime to voluntarily give up power.
The international envoy on Syria, the former United Nations secretary general Kofi Annan, has asked governments with influence to twist arms to halt the escalating violence.
His spokesman is Ahmad Fawzi.
AHMAD FAWZI: What we need to do is get the parties to respect the plan and implement the plan. The problem ain't the plan. The problem is implementation of the plan.
BRENDAN TREMBATH: Ahmad Fawzi says UN observers have spotted helicopters being used by government forces for the first time in the conflict.
AHMAD FAWZI: Our observers have videotaped helicopters in the skies with fire coming out of them. So, whether they are helicopters with machines guns or helicopter gunships, we have not been able to make that distinction yet; but yes, they are being used and we have observed them being used.
BRENDAN TREMBATH: He says it's a clear breach of the ceasefire which was meant to come into effect in April.
EMILY BOURKE: Brendan Trembath reporting from Washington.