AMMAN, Jordan - The United States and its partners will widen support for the Syrian rebels, potentially by sending more weapons or taking other measures short of sending U.S. forces, if diplomacy fails to end a civil war that has killed "upwards of 100,000" people, Secretary of State John Kerry said Wednesday.

With the Syrian rebels he is trying to help in disarray, Kerry lowered expectations for an international effort to draw rebels and a resurgent Syrian regime to the bargaining table.

"These are big stakes, and I don't have any illusions about how difficult it is to find that path forward," Kerry said, speaking in Amman ahead of a strategy session with key Western and Arab nations backing the rebels.

The goal is to arrange an international peace conference next month in Geneva, under U.N. auspices, to implement a cease-fire and begin forming a transitional government.

"In the event that we can't find that way forward, in the event that the Assad regime is unwilling to negotiate in good faith, we will also talk about our continued support and growing support for the opposition in order to permit them to continue to fight for the freedom of their country," Kerry said.

The United States and Russia, which back opposing sides in the conflict, have agreed to sponsor the meeting and lobby the rebels and President Bashar al-Assad's government to participate. The rebels have refused to commit to attending, while the government - which, Kerry acknowledged, has made military gains recently - has been more receptive.

"We're not here to dictate to them, or to anybody, an outcome," Kerry said of the fractured rebel leadership. He promised that the 11 nations meeting in Jordan would "listen to all voices" about the format, agenda and timing of the proposed peace conference but warned that the process, if it takes hold, will not be swift.

The alternative to seeking a peace agreement is continued killing, the empowerment of extremists and the possible disintegration of Syria, Kerry said. So no matter the odds, he said, it is important to try.