"Well, we haven't ever articulated a Plan B. People have talked about the possibility of a Plan B, obviously, if plan A fails. But nobody has laid out the elements of that plan at this point in time. There's been some public speculation about it," Kerry told the CTV television network in an interview released late on Wednesday, Sputnik News reported.
In February, Russia and the United States reached an agreement on the cessation of hostilities in Syria. The ceasefire took effect on February 27.
The agreement does not apply to groups operating in Syria that are designated as terrorist organizations by the United Nations.
Even before the ceasefire was implemented, Washington had expressed skepticism about the successful implementation of the agreement, warning that violations would likely occur that may necessitate reverting to a Plan B for Syria that could include the partitioning of the country.
Syria has been entangled in civil war since March 2011, with foreign-backed Takfiri terrorist groups like Daesh (ISIL) controlling parts of it, mostly in the east.
In the past five years, more than 260,000 people have died in Syria -overwhelmingly civilians- and around 4 million Syrians are now refugees in other countries. Around 8 million others have been displaced internally.