"Today, people can more clearly understand how alone Assad is in standing up for himself, not for Syria," Kerry said during a media availability at the Geneva II International Conference on Syria in Montreux, Switzerland. "And the resolution to this crisis cannot be about one man's insistence or one family's insistence about clinging to power. This needs to be about empowering all of the Syrian people."
Representatives of the more than 40 countries and organizations at the conference articulated in clear terms how the conflict must end, Kerry said.
"[It] has to have an inclusive Syria where every citizen can live in dignity, led by a government that the people of Syria empower with their consent," he said, meaning Assad cannot be a part of any transitional government.
"Let me reiterate what the United States, the Syrian opposition, and many others said this morning: No one should think for a moment that in the future of Syria there can be a place for a man who has turned on his own people, permitted the death of 130,000 many of them by his choice of weapons and others by his choice of their mission, because some of those deaths are obviously soldiers," Kerry said.
"You cannot have peace, you cannot have stability, you cannot restore Syria, you cannot save Syria from disintegration as long as Bashar Assad remains in power," Kerry said.
Kerry said he and Russian Foreign Minister Sergei Lavrov were pursuing "a number of things that we believe we can engage in that may or may not be able to have an impact" on discussions.
Without going into detail, he said "lots of different avenues will be pursued, including continued support to the opposition and augmented support to the opposition."
A political solution to the crisis in Syria would be take time, Kerry said.
"So it's up to all of us to do our best to try to make sure that Geneva and/or one of the parallel tracks works, and I'm not going to talk about the possibilities of it not finding some road forward."
The discussions began with a clash between U.S. and Syrian diplomats over Assad and whether he could rule Syria.
Top diplomats gathering in Switzerland for the international talks heard U.N. Secretary-General Ban Ki-moon urge all sides to grab the chance for peace, CNN reported.
"After nearly three painful years of conflict and suffering in Syria, today is a day of fragile but real hope," he said, kicking off the conference in Montreux.
In his opening statement, Kerry said there is "no way" Assad will be part of a transitional government in the war-torn country.
Lavrov disputed U.S. insistence that Assad not be part of a possible transitional administration, arguing that the conference must "refrain from any attempt to predetermine the outcome of the process," the New York Times reported.
Lavrov argued Iran, which supports the Assad regime as does Russia, should be at the conference. The United States opposed allowing Iran to participate until it publicly endorses the conference's mandate, and successfully pressed the United Nations to withdraw its invitation to the Islamic republic.
Syrian Foreign Minister Walid al-Muallem, who also clashed with Ban, said: "No one, Mr. Kerry, no one can grant or withdraw the legitimacy of the president other than the Syrians themselves. This is their right and duty."
Speaking for more than an hour instead of his allotted 7 minutes, Muallem accused Arab nations of financing terrorism and conspiring to destroy his country, the Times said.
"They have used their petrodollars to buy weapons," he said, "and to flood the international media with lies."
When Syrian National Coalition President Ahmad al-Jarba spoke, he denounced the Assad government and Iran, which has sent arms and troops to support Assad.
"We want to be sure we have a Syrian partner in this room." Jarba said. "Do we have such a partner?"
He said the opposition would never accept Assad being part of a transitional administration.
Diplomats were meeting in Switzerland to discuss how to address a conflict the United Nations estimates killed more than 100,000 people and displaced millions since the conflict began in March 2011.
The international session began Wednesday in Montreux but direct talks between the Syrian government and opposition delegations won't begin until Friday in Geneva.
The official objective of the peace talks, known as Geneva II, is to establish a process to create a transitional government with full executive powers that would run the country until elections can be held, likely excluding Assad. This was the objective worked out at an international conference on the Syria conflict, known as Geneva I, held in Geneva in June 2012.