The United States and Russia have announced plans for a cessation of hostilities in Syria that would go into effect at midnight on February 27.
In a joint statement issued on February 22, the two countries said that parties to the five-year-old conflict would indicate their agreement by midday on February 26, Damascus time.
However, the truce does not include the Islamic State group, the Al-Qaeda-linked Al-Nusra Front, and other terrorist organizations designated by the UN, and air strikes by Syria, Russia, and a U.S.-led coalition against these groups will continue, the statement said.
The agreement sets up a communications hotline, and calls for a working group to monitor cease-fire violations.
UN Secretary-General Ban Ki-moon welcomed the agreement as a "long-awaited signal of hope," and urged all sides to abide by it.
Syria's main opposition group, the Saudi-backed High Negotiations Committee, said it "agreed to respond positively to international efforts to reach a truce deal."
But its "commitment to the truce is conditional" on the lifting of sieges, an end to attacks on civilians, the freeing of prisoners and the delivery of aid, the group added.
Russian President Vladimir Putin and his U.S. counterpart, Barack Obama, discussed the plan by telephone.
In a statement broadcast on television, Putin called the accord a "real step that can stop the bloodshed" in Syria.
Russia will do "whatever is necessary" to ensure that Damascus respects the cease-fire agreement, Putin said. "We are counting on the United States to do the same with its allies and the groups that it supports."
"The main thing is that conditions have been created for launching a genuine political process through the wide inter-Syrian dialogue in Geneva overseen by the UN," the Russian president also said.
He added that the U.S.-Russia agreements "can be an example of responsible actions, based on the norms of international law and the principles of the UN, against the threat of terrorism."
Meanwhile, Kremlin spokesman Dmitry Peskov said Moscow "highly appreciates" the level of interaction of the Russian and U.S. experts in the negotiations of the cease-fire plan.
Russia -- Syrian President Bashar al-Assad's strongest ally -- and the United States back opposing sides in the Syria war.
The White House said that although it will be difficult to implement, the move presents a "moment of opportunity" and the United States will try to capitalize on it.
"If implemented and adhered to, this cessation will not only lead to a decline in violence, but also continue to expand the delivery of urgently needed humanitarian supplies to besieged areas," U.S. Secretary of State John Kerry said in a statement.
Turkey also welcomed the cease-fire plan, with Deputy Prime Minister Numan Kurtulmus expressing hope that Russia "won't fly its jets and kill innocent people" while the combatants negotiate over an end to the conflict.
British Foreign Secretary Philip Hammond said the truce will only work if there is a "major change of behavior" by the Damascus regime and its backers.
"Russia, in particular, must honor this agreement by ending its attacks on Syrian civilians and moderate opposition groups," Hammond said.
On February 12, major powers agreed to work toward a "cessation of hostilities" in Syria within a week, but the deadline passed.
Violence has continued in Syria, with more than 140 people killed in bombings in Damascus and Homs on February 21.
More than 250,000 Syrians have been killed in the conflict, which started in March 2011. About 11 million others have been forced from their homes, including 4 million who have fled abroad.
With reporting by AFP, AP, Reuters, TASS, and Interfax