WASHINGTON — The United States and Russia reached agreement on a partial Syria truce to go into effect Feb. 27, after intensive Russian-American negotiations in Geneva culminated in a phone call Feb. 22 between US President Barack Obama and Russian President Vladimir Putin.

Under the complex “cessation of hostilities” agreement, announced in a US-Russian joint statement after Obama and Putin spoke by phone, the warring Syria parties, with the exception of the Islamic State (IS) group and al-Qaeda-linked Jabhat al-Nusra, have until noon Feb. 26 Damascus time to inform the United States or Russia whether they intend to accept the truce deal.

Those Syrian parties and armed groups (minus IS and Jabhat al-Nusra) that accept the “cessation of hostilities” will not be targeted by the Syrian-, Russian- or US-led anti-IS coalition militaries, the joint agreement states. The United States and Russia, which co-chair the International Syria Support Group (ISSG) cease-fire task force, will map out where Jabhat al-Nusra, IS and other groups are and set up a communications hotline in order to try to adjudicate if and when there are violations of the truce terms, the State Department said, as officials acknowledged there were still procedural details to be finalized and much mistrust and skepticism about a way out after five years of brutal conflict.

“We are all aware of the significant challenges ahead,” Kerry said Feb. 22 in a statement welcoming the agreement. “This is a moment of promise, but the fulfillment of that promise depends on actions.”