The European Union and Russia have agreed that United Nations envoy Kofi Annan's faltering peace plan remains the best chance to bring calm to the troubled Middle East country, EU co-chief Herman Van Rompuy said on Monday.

At the same time, however, the EU-Russia Summit held in St. Petersburg Monday underscored the differences between the two parties with respect to the sources of violence in Syria and the role of President Bashar al-Assad's regime.

"The European Union and Russia might have some diverging assessments, but we fully agree that the Annan plan as a whole provides the best opportunity to break the cycle of violence in Syria," European Council President Van Rompuy told a news conference after talks with Russian President Vladimir Putin in St. Petersburg, as cited by RIA Novosti.

"We need to combine our efforts in order for this to happen, and to find common messages on which we agree," he added.

Putin, flanked by Van Rompuy and European Commission President Jose Manuel Barroso, made no statement on Syria at the news conference.

Van Rompuy, Barroso and EU foreign policy chief Catherine Ashton were among the diplomats attending Monday's scheduled summit, the first meeting between top level EU officials and Putin since his return to the Kremlin as Russian President last month.

The Kremlin has come under pressure to take a harder line on embattled Syrian President's Bashar al-Assad regime, which Western powers and Arab governments have accused of atrocities. Ashton called on Sunday Russia's role in attempts to end 15-months of bloodshed in Syria "crucial."

Russian news agency RIA Novosti reminds that Russia has denied that it is protecting Assad or that it has any special interests in Syria, but has twice – along with China - vetoed UN resolutions against Damascus over what it calls a pro-rebel bias. Moscow has, however, fully backed Annan's plan, which calls for the withdrawal of heavy weaponry from urban areas and a ceasefire to end 15-months of spiraling violence there.

Putin said in February in a pre-election campaign article that Russia would not allow a repeat of the "Libyan scenario." Russia abstained from the March 2011 UN Security Council vote on the resolution that led to NATO airstrikes against forces loyal to Libyan leader Muammar Gaddafi and his eventual death at the hands of rebels.

The St. Petersburg summit comes a day after Assad, in a televised address, denied that government forces were to blame for the May 25 massacre of over 100 people, including dozens of children, in the Syrian town of Houla. Assad said the killings were an "ugly crime" that even "terrorists" would balk at carrying out.

The United Nations, citing eyewitnesses, has said pro-Assad militia fighters were responsible for the slaughter. Russia has criticized Syria over its shelling of the town, but says it does not rule out that rebels carried out the majority of the killings as a "provocation" ahead of a visit by Annan to Syria.

But Putin insisted after talks with German Chancellor Angela Merkel on Friday that while Russia had "many years of good relations with Syria," those who accused Russia of supporting the Assad regime were "wrong." He also said that weapons Russia was supplying to Syria could not be used in a civil war.

Putin was speaking after U.S. Secretary of State Hillary Clinton said Russia's stance on Syria was leading to "civil war" there.