The United Nations and Arab League envoy to Syria is to convene a high-level meeting in Geneva amid the worsening situation in the Middle East.
The deputy for envoy Kofi Annan said he would hold an "action group on Syria" for June 30, seeking to find a "common position on proposed outcomes".
Jean-Marie Guehenno said the six-point plan forged by Mr Annan "is clearly not being implemented."
Mr Guehenno's statement to the UN Human Rights Council comes amid a report by UN investigators on the growing numbers of Syrians are being targeted in the country's conflict on account of their religion.
UN investigators said they suspect pro-government forces of many of the 108 killings committed in the massacre in the Syrian town of Houla in May.
The report said: "The Commission of Inquiry (COI) is unable to determine the identity of the perpetrators at this time, nevertheless the COI considers that forces loyal to the government may have been responsible for many of the deaths."
The council was also told that the foreign-backed Syrian armed opposition has tortured and executed soldiers amid an increasing use of improvised explosive devices in the conflict.
Meanwhile, Syrian president Bashar Assad has admitted his country is in state of war with rebel fighters and ordered his new cabinet to crush the anti-regime uprising.
The official Sana news agency quoted him as saying: "When one is in a state of war, all our policies and capabilities must be used to secure victory."
In the days before Mr Assad's comments, Sky's Stuart Ramsay spent time with Free Syrian Army (FSA) opposition fighters in the mountainous Bdama region near the Turkish border.
It is set to become the next battleground between the two sides and the FSA claims to have up to 2,000 men in the area, many of them from a non-military background who are being trained by defectors.
Ramsay said: "It's still pretty ragtag stuff but there's a semblance of a fighting force of sorts.
"They're certainly better organised than they have been in the past."
The US said a "desperate" Mr Assad was slowly losing his grip on power, citing recent defections and fighting raging increasingly close to Damascus.
As Mr Assad was addressing his cabinet, Turkey vowed to retaliate against Syria for the downing of one of its jets and Washington offered new support to its Nato ally after the incident.
White House spokesman Jay Carney said: "It is clear, however, that Assad is desperate to hang on to power at all cost, as evidenced by his continued use of air power and Shabiha gangs (pro-regime militia)."
On Wednesday, Turkish Prime Minister Recep Tayyip Erdogan backtracked after earlier saying his country had changed its rules of engagement and would treat any Syrian security threat as a military target.
Mr Erdogan said Turkey had no intention of attacking Syria.
The shooting down of the Phantom F-4 fighter jet had split Moscow and the West, with Nato condemning Syria and Russia saying the incident should not be seen as intentional.
Mr Erdogan, once a close ally of Mr Assad and now one of the Syrian leader's biggest critics, admitted the Turkish plane had violated Syrian airspace but said it was only for a short time and "by mistake", insisting that it was not in Syrian airspace when it was shot down.
Damascus has defended shooting down the jet, saying it was a response to "a gross violation" of its sovereignty.
After a request from Turkey, Nato’s secretary-general Anders Fogh Rasmussen hosted talks with ambassadors of the alliance's 28 members in Brussels.
"Allies have expressed their strong support and solidarity with Turkey," Mr Rasmussen said.
"We consider this act to be unacceptable and condemn it in the strongest terms."