Russia accused the West of seeking to distort an agreement for a political transition in Syria, after international peace envoy Kofi Annan said a ceasefire was imperative.
Russian Foreign Minister Sergei Lavrov hailed the Geneva accord based on proposals by Annan as an "important step" but said that Western capitals had read more into the final statement than what was written on paper.
"These (Geneva) agreements are not there to be interpreted. They mean exactly what is said in the communique and we need to follow the agreements that were made," he said.
His comments came soon after Annan spokesman Ahmad Fawzi told reporters a "shift" in positions by Russia and its diplomatic ally China at the Geneva talks should not be underestimated.
A two-day meeting of opposition groups which has been held behind closed doors in Cairo meanwhile ended late Tuesday with a consensus statement, according to Egypt's official MENA news agency.
The conference was boycotted by two of the largest groups -- the Syrian Revolution General Commission (SRGC) and the Free Syrian Army.
On Saturday, world powers agreed a plan for a transition in Syria that did not make an explicit call for President Bashar al-Assad to quit power, but the West swiftly made clear it saw no role for Assad in a unity government.
Meanwhile, French Foreign Minister Laurent Fabius said Russia will not attend a "Friends of Syria" meeting in Paris on Friday aimed at coordinating Western and Arab efforts to stop the violence in the country.
"Russia was invited. They made it known that they did not want to participate, which is not a surprise," he told reporters. Russia, a traditional ally of Syria, and China did not attend any previous meetings of the group.
In Washington, State Department spokeswoman Victoria Nuland said the Russians were free to decide whether to attend the Paris talks or not.
"It's their choice. We think this is a very valuable forum that brings together a much larger group of countries. The door is open to them if they want to join. It's up to them if they don't," Nuland told reporters.
"From our perspective, (this) meeting is important and will add energy and lift to this effort to come to a post-transition strategy" in Syria.
Secretary of State Hillary Clinton will lead the US delegation, an official said, with Nuland saying more than 100 countries would attend the talks "to support change and democracy and pluralism" in Syria.
The Paris meeting will be the third such gathering after one in Tunis in February and another in April in Istanbul called for tougher action against the Assad regime.
Annan said a real ceasefire was imperative in Syria, as the death toll mounted to 77 on Tuesday, according to monitors, nearly three months after a truce he brokered failed to take effect.
UN human rights chief Navi Pillay warned that foreign arms deliveries to both government and opposition are fuelling a conflict that rights monitors say has killed more than 16,500 people since March last year.
Pillay said both sides were guilty of "serious" rights violations, adding that "any further militarisation of the conflict must be avoided at all costs."
But a pro-Damascus Palestinian militant leader said the Lebanese Shiite militia Hezbollah and Iran would fight alongside the Syrian regime if it is attacked by foreign forces.
In the event of "a foreign attack, we discussed with our brothers (in the Syrian regime), with (Hezbollah chief) Hassan Nasrallah and our brothers in Iran, we will be part of this battle," said Ahmed Jibril of the Popular Front for the Liberation of Palestine-General Command.
Human Rights Watch documented 27 detention facilities across Syria it said were used to hold people swept up in the government's crackdown on an uprising now in its 16th month.
The group said it had carried out more than 200 interviews with former detainees, and military and intelligence defectors, "almost all" of whom described experiencing or witnessing torture, including "prolonged beatings, often with objects such as batons and wires."
Other methods included "holding the detainees in painful stress positions for prolonged periods of time, often with the use of specially devised equipment, the use of electricity, burning with car battery acid, sexual assault and humiliation, the pulling of fingernails and mock execution."
Meanwhile, as Turkey reported a new defection of Syrian troops across the tense border, Assad said he regretted "100 percent" that his country's defence forces shot down a Turkish fighter jet on June 22, but still insisted the plane was in Syrian airspace.
He rejected Turkey's accusations that the Syrian defence forces intentionally shot down the aircraft, which was on a training mission over the Mediterranean.
"A country at war always acts like this. This plane was flying at a very low altitude and was shot down by anti-aircraft defences which mistook it for an Israeli plane, which attacked Syria in 2007," Assad said in an interview with Turkey's Cumhuriyet newspaper"
Assad said Syria had no plans to send troops to the border with Turkey, even after Prime Minister Recep Tayyip Erdogan sent reinforcements to the frontier.
In Cairo, meanwhile, MENA reported that participants in the opposition conference "were unanimous that a political solution in Syria must begin with the departure of the regime of Bashar al-Assad."
They called for a end to the killing by the Syrian army and gave their support to the Free Syrian Army made up of deserters from the Assad regime force.
They also called on the Syrian army to lift its siege of Syrian towns and for the release of all detainees.