The United States will have to negotiate with Syrian President Bashar al-Assad for a political transition in Syria and explore ways to pressure him into agreeing to talks, US Secretary of State John Kerry has said.

In the interview broadcast on CBS News on Sunday, Kerry did not repeat the standard US line that Assad had lost all legitimacy and had to go. 

"We have to negotiate in the end," Kerry said. "We've always been willing to negotiate in the context of the Geneva I process," he added, referring to a 2012 conference which called for a negotiated transition to end the conflict.

Kerry said the US and other countries, which he did not name, were exploring ways to reignite the diplomatic process to end the conflict in Syria which is now in its fifth year.

Syria enters fifth year of conflict

"What we're pushing for is to get him [Assad] to come and do that, and it may require that there be increased pressure on him of various kinds in order to do that," the secretary of state said.

"We've made it very clear to people that we are looking at increased steps that can help bring about that pressure," he added.

But State Department spokeswoman Marie Harf said later that Kerry, in the interview with CBS, was not specifically referring to Assad. She reiterated that Washington would never negotiate with the Syrian leader.

Harf added: "By necessity, there has always been a need for representatives of the Assad regime to be a part of this process. It has never been and would not be Assad who would negotiate - and the Secretary was not saying that today."

The US led efforts to convene a UN-backed peace talks in Geneva last year between Western-backed Syrian opposition representatives and a government delegation. The talks collapsed after two rounds and no fresh talks have been scheduled.

Russian talks

Russia convened some opposition and government figures in January for talks on the crisis but they yielded little progress and the main opposition coalition boycotted them.

"To get the Assad regime to negotiate, we're going to have to make it clear to him that there is a determination by everybody to seek that political outcome and change his calculation about negotiating," Kerry said.

"That's under way right now. And I am convinced that, with the efforts of our allies and others, there will be increased pressure on Assad."

Syria sank into civil war after a peaceful street uprising against four decades of Assad family rule began in March 2011. The revolt spiralled into an armed insurgency, which has deepened with the rise of Islamic State of Iraq and the Levant (ISIL) and other armed groups.

Assad seems more likely to survive the Syrian crisis than at any point since it began. Iran's support for Assad is as solid as ever, with Russia showing no sign of abandoning him.

The war has killed more than 200,000 people and displaced close to half the population, according to the UN. Damascus accuses its Western and Gulf Arab opponents of seeking to destroy the country by providing aid to rebel groups.

Source: Agencies