MOSCOW/Geneva/BRUSSELS - Russian President Vladimir Putin said on Monday he was instructing his armed forces to start pulling out of Syria, over five months after he ordered the launch of a military operation that shored up his ally, Syrian President Bashar al-Assad.

"I believe that the task put before the defence ministry and Russian armed forces has, on the whole, been fulfilled," Putin said at a Kremlin meeting with his defence and foreign ministers at which he announced the withdrawal, starting on Tuesday.

Kremlin spokesman Dmitry Peskov said Putin had telephoned Assad to inform him of the Russian decision. The move was announced on the day United Nations-brokered talks between the warring sides in Syria resumed in Geneva.

Putin ordered an intensification of Russia's diplomatic efforts to achieve a peace deal to end the civil war in Syria, that has dragged on for five years, killed thousands of people and displaced millions, many of them seeking refuge in Europe.

But the Russian leader signalled Moscow would keep a military presence: he did not give a deadline for the completion of the withdrawal and said Russian forces would stay on at the port of Tartous and at the Hmeymim air base in Syria's Latakia province, from which Russia has launched most of its air strikes.

"With the participation of the Russian military ... the Syrian armed forces and patriotic Syrian forces have been able to achieve a fundamental turnaround in the fight against international terrorism and have taken the initiative in almost all respects," Putin said. "I am therefore ordering the defence minister, from tomorrow, to start the withdrawal of the main part of our military contingent from the Syrian Arab Republic."

By signalling the start of a withdrawal, Russia is likely to soothe tense relations with the United States, which has accused the Kremlin of inflaming the Syrian conflict and pursuing its own narrow interests.

"I think we did it to show the Americans that we do not have military ambitions and don't need unnecessary wars," said Ivan Konovalov, director of the Center for Strategic Trend Studies in Moscow. "They have been accusing us of all kinds of things and this is a good way of showing them they are wrong."

Putin said the naval base at Tartous and the Hmeymim air base "will function as they did previously. They must be reliably protected from land, sea and air".

Meanwhile, the European Union foreign ministers said Monday the bloc must stand up to Russia to defend core political and security interests but can still try to find common cause on issues such as the Syrian conflict,.

The ministers gathered in Brussels for a regular monthly meeting which for the first time in a year reviewed relations with Moscow which have been strained to breaking point by the Ukraine crisis.

EU foreign affairs head Federica Mogherini, who as Italian foreign minister before taking up her EU post in 2014 was widely seen as backing closer links with Russia, said they had "unanimity among the 28" on five broad principles.

First, Moscow must fully respect and implement the Minsk ceasefire accords in Ukraine and Brussels would not recognise its "illegal" 2014 annexation of Crimea, Mogherini told a closing press conference. The 28-nation bloc should boost ties with other east European and central Asian countries, many ruled from Moscow during the Soviet era, and strengthen EU resilience in areas such as energy where Russia is a key supplier for many member states, she said.

On the other side of the coin, ministers recognised "the need for selective engagement with Russia on foreign policy issues such as Iran, the Middle East, Syria... but also in other areas where there is a clear EU interest," she said.

The bloc will also seek to boost contacts with Russian civil society, especially with youth, Mogherini added. British Foreign Secretary Philip Hammond said as he arrived for the meeting that the EU should be under no illusions about Russia.

"We have to have relationships with Russia but we can't lose sight of the challenge that Russia represents to our values and to our security, and we have to be robust in making our case and defending our principles, our values and our borders in Europe," Hammond said.

On the other hand, talks to end Syria's civil war opened in Geneva on Monday, but hopes for a breakthrough remained remote with the sides locked in a bitter dispute over the future of President Bashar al-Assad. The UN-hosted negotiations, which began a day before the fifth anniversary of the outbreak of the conflict, are the latest effort to end violence that has killed more than 270,000 people and displaced millions.

As the delegations arrived in Geneva over the weekend, Damascus warned that any discussion about removing Assad would be a "red line".

Top Western diplomats immediately condemned the comment from Syrian Foreign Minister Walid Muallem as divisive and provocative.

After his first official meeting with the regime on Monday, UN envoy Staffan de Mistura told reporters that "strong statements (and) rhetoric" were part of every tough negotiation and that his initial discussions with government representative Bashar al-Jaafari were "useful".

Speaking earlier, he said the talks quickly needed to focus on "the real issues". "What is the real issue?" he asked. "The mother of all issues (is) political transition." The UN envoy said the agenda for the negotiations will follow a Security Council resolution that calls for a transitional government to be formed in six months, and general elections within the following year.

A lot has changed since the last round of indirect talks collapsed in February, particularly for many of Syria's war-ravaged people who have previously been deprived of regular access to life-saving aid.

A temporary ceasefire introduced on February 27 has largely held, despite accusations of violations from both sides, allowing aid to reach some 150,000 people living under siege.

The truce - the most significant since the conflict began - has sparked cautious encouragement. But experts warn that negotiations will still struggle to achieve a durable peace on the fractured battlefields where multiple groups are competing for dominance.

Representatives from Syrian Kurdish groups, which have played a key role in combatting jihadist fighters, have been excluded from the talks despite a push from Russia.

Russian Foreign Minister Sergei Lavrov reaffirmed Moscow's position on Monday, saying that "the whole spectrum of Syrian political forces" should have a voice in Geneva. "Otherwise this cannot claim to be a representative forum," he was quoted as saying by the RIA Novosti state news agency.

Beyond the contentious issue of Kurdish participation, Damascus has during previous peace efforts sought to veto various opposition figures and branded others as "terrorists".

Jaafari said he pressed the point again with de Mistura on Monday, asking for details of those invited and whether "all the delegations have been treated with equal criteria."

"The rule of the game will be inclusiveness," de Mistura said, adding that he was open to broadening the list of delegates as early as this round of negotiations, which is expected to last until March 24.

A second round of roughly two weeks of talks would start after a brief recess, followed by third round, at which point de Mistura said he hoped there would be a "clear roadmap" for a permanent deal.

The UN envoy acknowledged the huge divisions between the opposing sides, with Assad's fate and the prospect of holding elections standing out a key hurdles. But, he stressed, walking away from dialogue was not an option.

"As far as I know, the only plan B available is the return to war, and to an even worse war than we had so far," he said.