WASHINGTON (REUTERS) - U.S. Secretary of State John Kerry insisted on Friday Syrian President Bashar al-Assad has no place in Syria's future and said the United States was not without options on stepping up pressure on him.

Mr Kerry will lead a U.S. delegation to Switzerland next week for peace talks between the Syrian government and rebels aimed at ending the country's civil war. His comments also come as Syrian opposition groups vote on whether to attend the U.N.-sponsored talks in Montreux, Switzerland.

"I believe as we begin to get to Geneva, and begin to get into this process, that it will become clear there is no political solution whatsoever if Assad is not discussing a transition and if he thinks he is going to be part of that future. It is not going to happen," Mr Kerry told a news conference after meetings with his Canadian and Mexican counterparts.

"We are also not out of options with respect to what we may be able to do to increase the pressure and further change the calculus," he added.

Syria sank into civil war after a peaceful street uprising in March 2011 against four decades of Assad family rule. The revolt spiraled into an armed insurgency after the army responded with massive and deadly force to suppress the unrest.