Bashar Al Assad will not be ruling Syria in the future and Russia's military interventions will not help him stay in power, Saudi Arabia's Foreign Minister Adel al-Jubeir told a German newspaper in an interview published on Saturday.

"There will be no Bashar al-Assad in the future," al-Jubeir told newspaper Sueddeutsche Zeitung.

"It might take three months, it might take six months or three years - but he will no longer carry responsibility for Syria. Period."

Saying that the Syrian people's determination to topple Assad was unbroken despite heavy Russian air strikes and persecution within the country, Al Jubeir criticised Russia's involvement in the five-year-long war.

Earlier on Friday, the Saudi minister, in an exclusive televised interview with CNN's Christiane Amanpour, said: "A man who's responsible for the murder of 300,000 plus people, the displacement of 12 million people, the destruction of a country, is a man with absolutely no future in this country."

"Assad will leave, have no doubt about it. He will either leave by a political process or he will be removed by force. The Syrian people will not accept him being in power," he added.

He said that Assad's previous calls for help to his own military, Iran, Hezbollah and Shiite militia forces from Iraq and Pakistan were all in vain.

"Now he called the Russians, but they won't be able to help him either,"Al Jubeir said.

Russia entered the war on September 30 2015 in support of the Syrian president. At least 250,000 people have been killed, 11 million made homeless and hundreds of thousands have fled to Europe since the conflict began in 2011.

Moscow has said its air strikes are against the extremist militant groups Islamic State and the Nusra Front, but other countries and rebel groups say the attacks target civilians.

Asked about a more direct military involvement with 'boots on the ground', Al Jubeir said such discussions were currently underway among the member states of a US-led coalition against the Islamic State.

"If the coalition should decide to deploy special forces in the fight against IS in Syria, Saudi-Arabia will be ready to participate," he said, using the initials IS to refer to Islamic State.

At a peace and security conference in Munich, major powers agreed on Friday to a pause in combat in Syria, but Russia pressed on with bombing in support of its ally Assad, who vowed to fight until he regained full control of the country.

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 favour of Assad.

US 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."

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," Stoltenberg said.

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.

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 Russia 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 organisations," he said.

Britain and France said a peace deal could be reached only if Russia stops bombing insurgents other than Islamic State.

Meanwhile, two Syrian rebel commanders told Reuters they had been sent "excellent quantities" of ground-to-ground Grad missiles with a range of 20 km 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 centre. Some of the vetted groups have received military training overseen by the US Central Intelligence Agency.

The US has been leading its own air campaign against Islamic State fighters since 2014. US Defense Secretary Ash Carter said on Friday he expected Saudi Arabia and the UAE to send commandos to help recapture Islamic State's eastern Syrian stronghold, Raqqa.

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 urgent humanitarian aid.

"Convoys can go very soon if and when we have the permission and the green light from the parties," said Jan Egeland, head of the Norwegian Refugee Council, who chaired the meeting in Geneva.-Reuters