Upcoming peace talks on a political transition in Syria will test whether Syrian President Bashar al-Assad can negotiate in good faith, U.S. Secretary of State John Kerry said on Tuesday before a new round of negotiations in Geneva.

Assad has said he thinks the Geneva talks can produce a new Syrian government that includes opposition, independents and loyalists, but has rejected the idea of a transition authority.

But Syria’s opposition has consistently said it wants a halt in attacks on civilians and for the Geneva talks to result in a transitional governing body for Syria that does not include Assad.

“The key right now is whether Assad is capable of negotiating in good faith, and we have to put that to the test,” Kerry told Bloomberg Television in New York.

In Geneva, U.N. spokesman Ahmad Fawzi told reporters the second round of peace talks was expected to resume on Monday in Geneva. U.N. mediator Staffan de Mistura was in Moscow on Tuesday to prepare for the talks.

State Department spokesman Mark Toner said the expectation was that the next round would tackle “the core” issue of a political transition in Syria, including Assad’s future.

Kerry, who is working with Russia to persuade Assad to step down, said there was no way to end the Syrian war with Assad still at the helm.

“I don’t see any way possible for Assad to remain because there is no way to end the war while he is there, there is no way to end the violence, there is no way for him to unify the country,” Kerry said, “so Iran and Russia, and others need to recognize if you want peace, Assad has to transition.”