Secretary of State John Kerry on Wednesday said there was “no way” Syrian President Bashar Assad could have a role in any transitional government as negotiators met in Montreux, Switzerland to begin a new round of talks aimed at ending Syria's civil war.

“There is no way - no way possible in the imagination - that the man who has led the brutal response to his own people could regain the legitimacy to govern,” said Kerry in his opening remarks at the Syria peace talks.

“One man and those who have supported him can no longer hold an entire nation and a region hostage. The right to lead a country does not come from torture, nor barrel bombs, nor Scud missiles. It comes from the consent of the people,” he continued. “And it’s hard to imagine how that consent could be forthcoming at this point in time.”

Top diplomats are meeting in Montreux to reach an accord implementing the Geneva road map to peace, which hopes to end the three-year violent struggle between Assad and opposition forces seeking his ouster. The bloody civil war has left 100,000 dead and sparked a humanitarian crisis.

But Kerry’s comments only highlighted the difficulty ahead for negotiators. At an earlier conference in Geneva, diplomats agreed to a framework calling for a transitional government and free elections. But the international community faces a tough road ahead with Assad and opposition leaders far apart on how to achieve those goals.

In combative remarks, Syrian Foreign Minister Walid al-Moallem accused Western powers of funneling arms to rebel groups, calling the international community “interlopers,” according to reports and said that only the Syrian people would determine Assad’s role.

Sergei Lavrov, the foreign minister of Russia, one of Assad's chief backers, insisted that the talks did not have a predetermined outcome of removing the Syrian strongman from power. But Kerry insisted that Assad's attacks on civilians ruled out any future role, highlighting the sharp differences between the two sides.

The peace talks were almost derailed before their start after United Nations Secretary General Ban Ki-moon surprised the U.S. by extending an invitation to Iran to join the conference. That moved sparked protest from the Obama administration, which said that Iran, a supporter of Damascus, did not support key elements of the Geneva road map. Syrian opposition groups also threatened to boycott if Iran participated.

The crisis was averted after Iran admitted that it did not support the Geneva call for a transitional government in Syria and Ki-moon withdrew the invitation.

Kerry on Wednesday acknowledged the challenges ahead for negotiators.

“Today is a beginning. It’s a beginning of what will obviously be a tough and complicated negotiation,” said the secretary of state. “Peace talks to end a war and to end a struggle like this always are tough.”

But he insisted that the international community was “determined as ever to implement the Geneva communique.”