• Libya reportedly has all remaining chemical weapons removed by British and Danish Navy
• Denmark proposes withdrawal of chemical weapons from Libya

Meanwhile, political analyst Ammar Waqqaf has cast doubt on the sincerity of Kerry's assertion that "going on Al-Nusra" was never a negotiating point.

"United States have made a big decision in ditching Jabhat Al-Nusra to preserve the other fighting groups, the other what they call the moderate fighting groups," the analyst told RT, calling it the "cornerstone" of the deal.

Waqqaf is sure that Washington's move was prompted by the rapid advance of Syrian armed forces on rebel positions, which would have imminently led to the "severe deterioration" of the so-called moderate forces and hardline terrorist groups, including Al-Nusra, alike.

The decision to turn away from the most radical groups was made "to try and tie the Syrian state hand and Russian hand, in order to preserve the other groups who are less extremist but still extremist but they would call them moderate know," to preserve less extremist rebels.

The recent Al-Nusra rebranding when the militant group formally severed all ties with Al-Qaeda and changed its name to Jabhat Fateh al-Sham could have resulted in its inclusion into the moderate opposition if Washington had not strived to find a compromise with Russia, Waqqaf said.

For its part, the Saudi-backed High Negotiating Committee (HNC) issued a statement welcoming the split and encouraging the former Al-Nusra group to commit to further reforms.

"Saudi Arabia saw an opportunity to bring Jabhat Al-Nusra, which is a formidable fighting force under their umbrella, and tried to tell the Americans: Look, we can turn this into real moderates and you do not have to bomb them."

However, "Americans knew that there would be no deal with Russian unless Jabhat Al-Nusra is called Jabhat Al-Nusra, Al-Qaeda and that they are separate [from moderate rebels]."

Turkey ... said it supported the deal and was preparing humanitarian relief for Aleppo.

The European Union's top diplomat, Federica Mogherini, welcomed the Syria truce and called on the UN to act on it. "The agreement... is very welcome. All parties to the conflict, other than groups designated as terrorist organizations by the United Nations Security Council, must now ensure its effective implementation," she said.

The UN's special envoy for Syria, Staffan de Mistura, also welcomed the truce agreement, saying it provides "clear rules" for a cessation of hostilities.

German Foreign Minister Frank-Walter Steinmeier called for prompt implementation of the truce. "I call on parties to the conflict in Syria and in the region to stick to the agreement reached by Washington and Moscow and stop fighting on Monday at the latest," he said in a statement released by his office.

Statements supporting the US-Russian plan also came from officials of other European countries, such as France, Sweden, and Norway.

An ambiguous expression of support came from the UK, however. Foreign Secretary Boris Johnson said he welcomed the ceasefire, but lashed out at the government in Damascus, equating it with terrorist forces in terms of the violence it wrought, calling them the "twin scourges" of Syria. "I call on all parties to the Syria conflict and all countries with influence upon them to do what is needed to end violence and lift sieges," he said in a statement. "In particular, it's vital that the regime in Damascus now delivers on its obligations, and I call on Russia to use all its influence to ensure this happens. They will be judged by their actions alone."

Similarly veiled skepticism was expressed by the Pentagon, which said it would not begin the promised cooperation with Russia until Damascus observes the ceasefire in full. "Those commitments must be fully met before any potential military cooperation can occur," Pentagon spokesman Peter Cook said. "We will be watching closely the implementation of this understanding in the days ahead."