By John Davison
BEIRUT (Reuters) - President Vladimir Putin's overture to opponents of Russia's bombing campaign in Syria was snubbed on Monday, with Saudi sources saying they had warned the Kremlin leader of dangerous consequences and Europe issuing its strongest criticism yet.
Nearly two weeks since joining the 4-year-old war in Syria, Putin took his biggest step to win over regional opponents, meeting Saudi Defence Minister Mohammed bin Salman on the sidelines of a Formula One race in a Russian resort on Sunday.
Russian Foreign Minister Sergei Lavrov said on Monday that those talks, along with discussions with the United States, had yielded progress on the conflict, although Moscow, Washington and Riyadh did not agree in full "as yet".
But a Saudi source said the defense minister, a son of the Saudi king and one of the chief architects of its regional policy, had told Putin that Russia's intervention would escalate the war and inspire militants from around the world to go fight.
Riyadh would continue to support Assad's opponents and demand that the Syrian leader leave power, the source said, speaking on condition of anonymity while describing the talks with the Russians.
European foreign ministers, meeting in Luxembourg, issued a statement calling on Moscow to halt its bombing of Assad's moderate enemies immediately.
"The recent Russian military attacks ... are of deep concern and must cease immediately," ministers said in their most strongly-worded statement on Russia's intervention in a war which has claimed the lives of 250,000 people and caused a refugee crisis in neighboring countries and Europe.
"The military escalation risks prolonging the conflict, undermining a political process, aggravating the humanitarian situation and increasing radicalization," said the ministers.
Moscow says it is targeting only banned terrorist groups in Syria, primarily Islamic State. In its daily briefings, it describes all of the targets it strikes as belonging to Islamic State, although most of them have taken place in parts of the country held by other opposition groups, including many that are supported by Arab states, Turkey and the West.
For the first time since World War Two, Russian forces are flying combat missions in the same air space as Americans, who are leading a military coalition of Western and regional countries that is also bombing Islamic State.
Those countries say Assad's presence makes the situation worse and he must leave power in any peace settlement. They accuse Moscow of using Islamic State as a pretext to bomb other enemies of Assad, charge denied by Russia.
Syrian forces and their allies from the Lebanese Shi'ite militia Hezbollah, backed by Iranian military officers, have launched a massive ground offensive in coordination with the Russian air support.
They fought their fiercest clashes on Monday since the assault began, advancing in strategically important territory near the north-south highway linking Syria's main cities.
Russian warplanes carried out at least 30 air strikes on the town of Kafr Nabuda in Hama province in western Syria, and hundreds of shells hit the area as the Syrian army and Hezbollah fighters seized part of it, according to the Syrian Observatory for Human Rights, which monitors the conflict.
The Observatory and Lebanon-based al-Mayadeen television station said the pro-government forces captured the southern part of the town on Monday.
"These are the most violent battles in the northern countryside (of Hama) since the start of joint operations several days ago" between the Russian air force and Syrian ground forces, said the Observatory's Rami Abdulrahman.
Syria's army chief of staff was cited by the state news agency as saying forces had taken control of Kafr Nabuda. Capturing the town would bring government forces closer to insurgent-held positions along the main highway that links Syria's main cities.
Russia said it carried out 55 sorties and hit 53 of what it described as Islamic State targets in the last 24 hours.
The Syrian army and Hezbollah on Sunday took control of Tal Skik on the other side of the highway in southern Idlib province. Many of Russia's air strikes have hit the surrounding area, which also lies east of Assad's stronghold Latakia.
The Russian intervention in Syria has wrongfooted the U.S. administration of President Barack Obama, which has been trying to defeat Islamic State while still calling for Assad's downfall.
Last week, Washington shelved a program to train and equip "moderate" rebels opposed to Assad who would join the fight against Islamic State. The only group on the ground to have success against Islamic State while cooperating with the U.S.-led coalition is a Kurdish militia, the YPG, which has carved out an autonomous zone in northern Syria and advanced deep into Islamic State's stronghold Raqqa province.
On Monday, the YPG announced a new alliance with small groups of Arab fighters, which could help deflect criticism that if fights only on behalf of Kurds. Washington has indicated that it could direct funding and weapons to Arab commanders on the ground who cooperate with the YPG.
(Additional reporting by William Maclean in Dubai, Tom Perry in Beirut, Gabriela Baczynska in Moscow and Robin Emmott in Luxembourg; Writing by Peter Graff, editing by Peter Millership)