A deal to implement a ceasefire in Syria's almost five-year civil war has been reached between Russia and the US, President Vladimir Putin said late on February 22 in a nation-wide televised address that interrupted regular programming on the state Rossiya-1 TV network.

The cessation of hostilities in the conflict that has claimed upwards of 250,000 lives and in which Russia and the US support opposing sides, is due to come into effect at midnight Damascus time on February 27. Before then, all active military groups in Syria must relay their commitment to the truce to either country.

"I have just completed a telephone conversation with the US President Barack Obama," Putin said, adding that "the conversation was initiated by the Russian side, but the interest was certainly mutual".

"I am convinced that joint efforts agreed with the US [to ensure the cessation of hostilities] are capable of turning the tide most radically in settlement of the Syria crisis," Putin said, hailing "a real chance to stop the longstanding bloodshed and violence". He added that the truce would create conditions for "the launch of a real political process in the format of a broad intra-Syrian dialogue in Geneva under the auspices of the UN".

The announcement marks Putin's ongoing effort to establish Russia as a strong regional player with its military air campaign in the Syrian conflict launched in September 2015, amid Western accusations that Russian air strikes more often target civilians and political opponents of  Syrian President Bashar al-Assad than the so-called Islamic State (IS) and other terrorist groups.

Under the ceasefire terms, the Russian military, the US-lead coalition, and Assad's forces pledge not to attack any groups except IS, the Nusra Front and other terrorist organisations defined by the UN Security Council.

Putin recalled the "positive experience" of joint cooperation in eliminating chemical weapons in Syria, which proved useful in the intense "closed consultations" of Russian and US negotiators in the lead-up to the ceasefire.

Assad on board

On February 23, the Syrian government said it agreed to halt its combat operations and will coordinate with Russia on which areas and groups to include in the ceasefire, while stressing the requirement to seal the borders and halt inflow of resources to armed groups.

It remains unclear how anti-Assad opposition groups supported by the US and Europe will be treated under the agreement by Russia and the Syrian government. However, these do not directly fall into the category of those excluded from the ceasefire under Putin's definition.

Syria's main opposition bloc, the High Negotiations Committee (HNC) backed by Saudi Arabia, said it will accept the ceasefire deal, while stressing it would remain conditional to the commitment of the Assad regime and its allies Russia and Iran "to stop hostile acts".

Conditions set forward by the HNC include the release of prisoners, delivery of humanitarian aid, and stopping the sieges and the bombardment of civilians.

Cautious US welcome

Although the possibility of a truce was welcomed in Russia, the US and the UN, White House press secretary Josh Earnest said the deal "is going to be difficult to implement", reminding that a diplomatic solution had previously failed for years.

While critics say the exception in the truce for attacks on IS creates a loophole likely to be exploited by the sides for other purposes, UN officials tried to put a positive spin on the fragility of the situation.

"I think the danger that this could turn into something even more dangerous unites everyone right now," UN Deputy Secretary General Jan Eliasson said.

Turkey also welcomed the ceasefire plan, with Deputy Prime Minister Numan Kurtulmus saying he hoped Moscow will now stop carrying out air strikes in support of the Syrian government.

"We hope all the groups in Syria, including the moderate opposition, will take part in rebuilding Syria at the end of the negotiations that will continue for six months," Kurtulmus added.