BRUSSELS: The European Union's senior diplomat said on Monday there was no Cold War climate between Moscow and the West as they agreed to a pause in the fighting in Syria, although Russia's prime minister said tension was growing.

At a security conference in Munich on Friday, world powers agreed to a "cessation of hostilities" that would let humanitarian aid be delivered in Syria and was envisaged to start this week.

But a day later Russian Prime Minister Dmitry Medvedev told the gathering that Moscow and the West had "fallen into a new Cold War".

"I have not seen the climate of Cold War in these last days," EU foreign policy head Federica Mogherini said when asked to comment on the Russian warning. She urged all the parties to the Syria agreement to stick to their commitments.

But Russia, Damascus' main foreign ally, has yet to stop its air strikes, which support the advance of government troops and allied militias on Syria's largest city, Aleppo.

Speaking in Brussels on Monday, Iranian Foreign Minister Mohammad Javad Zarif denied that backers of Syrian President Bashar al-Assad -- which include Teheran -- were using the revived diplomacy around Syria as a cover to pushing for more military advances on the ground.

"We're not trying to use diplomacy to gain anyting, but at the same time people cannot use diplomacy in order to provide human shield for al-Nusra and Islamic State working as a leverage," Zarif told a news conference with Mogherini, refering to the radical Islamist militias.

"What we agreed in Munich is a cessation of hostilities, not a pause to allow the allies of certain regional players to regroup," he said in criticism of Iran's foe Saudi Arabia.

Sunni power Saudi Arabia opposes Assad, as well as Islamic State. Riyadh has said it was ready to participate in a ground operation in Syria if the U.S.-led coalition fighting Islamic State there decides to start one.

New hostilities have also broken out between Turkey and the Kurdish YPG militia since Munich, prompting Berlin to urge restraint.

"As part of the Munich Agreement...all sides are called on - even before the start of a ceasefire - to contribute to an immediate reduction in violence," German Foreign Minister Frank-Walter Steinmeier said.

"That goes for Russia and the Syrian regime's military operations around Aleppo and the latest attacks by PYD militias in northern Syria. In view of the tense situation, Turkey too must show restraint."

The war in Syria has killed at least 250,000 people as Assad, the rebels seeking to oust him, and the foreign backers of the rival sides have failed to agree on ways to end the conflict, which created a breeding ground for radical Islamists.