By John Irish and Warren Strobel
MUNICH/AMMAN (Reuters) - Major powers agreed on Friday to a pause in combat in Syria, but Russia pressed on with bombing in support of its ally President Bashar al-Assad, who vowed to fight until he regained full control of the country.
Although billed as a potential breakthrough, the "cessation of hostilities" agreement does not take effect for a week, at a time when Assad's government is poised to win its biggest victory of the war with the backing of Russian air power.
If implemented, the deal hammered out at five hours of late night talks in Munich would allow humanitarian aid to reach besieged towns. It was described by the countries that took part as a rare diplomatic success in a conflict that has fractured the Middle East, killed at least 250,000 people, made 11 million homeless and sent hundreds of thousands fleeing into Europe.
But several Western countries said there was no hope for progress without a halt to the Russian bombing, which has decisively turned the balance of power in favor of Assad.
U.S. Secretary of State John Kerry said that if the peace plan fails, more foreign troops could enter the conflict.
"If the Assad regime does not live up to its responsibilities and if the Iranians and the Russians do not hold Assad to the promises that they have made...then the international community obviously is not going to sit there like fools and watch this. There will be an increase of activity to put greater pressure on them," Kerry, who was in Munich, told Dubai-based Orient TV.
"There is a possibility there will be additional ground troops."
U.S. President Barack Obama has ruled out sending U.S. ground troops to Syria, but Saudi Arabia this month offered ground forces to fight Islamic State.
Rebels said the town of Tal Rifaat in northern Aleppo province was the target of intensive bombing by Russian planes on Friday morning. The British-based Syrian Observatory for Human Rights, a monitoring body, said warplanes believed to be Russian also attacked towns in northern Homs.
The news agency AFP quoted Assad as saying he would continue to fight terrorism while talks took place. He would retake the entire country, although this could take a long time, he said.
Another week of fighting would give the Damascus government and its Russian, Lebanese and Iranian allies time to press on with the encirclement of Aleppo, Syria's biggest city before the war, which they are now on the verge of capturing.
They are also close to sealing the Turkish border, lifeline of rebel territory for years.
Those two victories would reverse years of insurgent gains, effectively ending the rebels' hopes of dislodging Assad through force, the cause they have fought for since 2011 with the encouragement of Arab states, Turkey and the West.
The cessation of hostilities agreement falls short of a formal ceasefire, since it was not signed by the main warring parties - the opposition and government forces.
Implementing it will now be the key, Kerry said: "What we need to see in the next few days are actions on the ground."
Two Syrian rebel commanders told Reuters they had been sent "excellent quantities" of ground-to-ground Grad missiles by foreign backers in recent days to help confront the Russian-backed offensive.
Foreign opponents of Assad including Saudi Arabia and Turkey have been supplying vetted rebel groups with weapons via a Turkey-based operations center. Some of the vetted groups have received military training overseen by the U.S. Central Intelligence Agency.
Russia suggested it might not stop its air strikes, even when the cessation of hostilities takes effect in a week.
Foreign Minister Sergei Lavrov said Moscow would not stop bombing fighters from Islamic State and a rebel group called the Nusra Front, which is affiliated with al Qaeda, neither of which were covered by the cessation deal: "Our airspace forces will continue working against these organizations," he said.
Moscow has always said that those two jihadist groups are the principal targets of its air campaign. Western countries say Russia has in fact been mostly attacking other insurgent groups. Nusra fighters often operate in areas where other rebel groups are also active.
Turkey's foreign minister said on Friday Russia was targeting schools and hospitals in Syria.
NATO Secretary General Jens Stoltenberg said Moscow must halt strikes on insurgents other than Islamic State for any peace deal to work.
"Russia has mainly targeted opposition groups and not ISIL (Islamic State). Air strikes of Russian planes against different opposition groups in Syria have actually undermined the efforts to reach a negotiated, peaceful solution," he said.
Britain and France said a peace deal could only be reached if Moscow stops bombing insurgents other than Islamic State.
The complex, multi-sided civil war in Syria has drawn in most regional and global powers, producing the world's worst humanitarian emergency and attracting jihadist recruits from around the world.
The United States has been leading its own air campaign against Islamic State fighters since 2014, when that group, also known as ISIS or ISIL, swept through much of eastern Syria and northern Iraq, declaring a caliphate.
U.S. Defense Secretary Ash Carter said on Friday he expected Saudi Arabia and the United Arab Emirates to send commandos to help recapture Islamic State's eastern Syrian stronghold, Raqqa.
Assad said he believed Saudi Arabia and Turkey were planning to invade his country. Russia has said Saudi ground troops would make the war last forever.
Saudi Arabia's foreign minister said the main objective in Syria was still to remove Assad, and "we will achieve it".
The main battlefields in the civil war are in the west of the country, far from Islamic State's strongholds, where Washington has largely steered clear, leaving the field to Russia which began its air campaign on Sept. 30 last year.
Kerry had entered the Munich talks pushing for a rapid halt to fighting, with Western officials saying Moscow was holding out for a delay.
The tactic of agreeing to a break in hostilities while battling for gains on the ground is one Moscow's allies used in eastern Ukraine only a year ago. A ceasefire there eventually took hold, but only after Russian-backed separatists overran a besieged town after the deal was reached.
Diplomats from countries backing the plan met on Friday to discuss sending in urgent humanitarian aid.
"I sense now that all of the ISSG (International Syria Support Group) members want to get aid to the besieged areas and also the hard-to-reach areas," said Jan Egeland, the head of the Norwegian Refugee Council, who chaired the meeting in Geneva.
"Convoys can go very soon if and when we have the permission and the green light from the parties."
The group, which includes Russia and Iran, had given "excellent feedback" and would meet again on Wednesday, Egeland told reporters after the 3 hour meeting.
The sides in Munich called for a resumption of political peace talks, which collapsed last week in Geneva before they began after the opposition demanded a halt to bombardment.
Syria's main opposition alliance cautiously welcomed the plan, but said it would not agree to join political talks unless the agreement proved effective.
World powers all say they support a "political transition", but there has been disagreement for years over whether that requires Assad to leave power, as Western countries have been demanding in vain since 2011.
A senior French diplomat said it would be Moscow's fault if it kept bombing and the peace process failed: "The Russians said they will continue bombing the terrorists. They are taking a political risk because they are accepting a negotiation in which they are committing to a cessation of hostilities.
"If in a week there is no change because of their bombing, then they will bear the responsibility."
(Additional reporting by Denis Dyomkin, Shadia Nasralla, and Robin Emmott in Munich, and Suleiman al-Khalidi in Amman; writing by Peter Graff and Anna Willard; editing by Andrew Roche)