"We would like to save lives, not see them caught up in a continued war," Kerry said. "But we are clear about whom we support in the effort to restore freedom and unity to the people of Syria."
The United States and its Western allies pledged new aid to the Syrian opposition coalition Thursday following a Friends of Syria meeting in Rome. The pledge includes $60 million in immediate aid, providing food, medical supplies and "direct, non-lethal aid" to rebel military forces.
Syrian rebel chief Salim Idris says his fighters need weapons from the United States, not food and bandages.
Idris told The Associated Press that he needs anti-tank and anti-aircraft missiles to stop President Bashar al-Assad's forces from annihilating the Syrian people. He said the non-lethal aid the United States plans to send to the rebels will not bring them any closer to victory.
Picture gallery of first overseas trip of Kerry as Secretary of State
The White House says President Barack Obama telephoned Russian President Vladimir Putin Friday to talk about Syria and other issues. It said the two presidents agreed it is important for Kerry and Foreign Minister Sergei Lavrov to continue to stay engaged on Syria.
During a European tour this week, Kerry warned Syrian President Bashar al-Assad that time for a peaceful solution is running out.
"The international community is not going to stand for Scuds [missiles] being fired indiscriminately against innocent civilians - women and children, young people - destroying the cities of Syria," he said. "That is unacceptable."
Kerry praised Turkey for its humanitarian efforts in helping Syrian refugees.
Earlier Friday, Russia said the decisions made at the Friends of Syria meeting won't help end the nearly two-year-long civil war.
Russia's foreign ministry said the decisions announced at the meeting in Rome would "directly encourage extremists" to seek power in Syria.
Opposition groups Friday reported fresh violence across Syria.
The Britain-based Syrian Observatory for Human Rights reported the bodies of 10 men were found dumped near a farm outside the the capital, Damascus. It says one man was decapitated and others were shot in the head. Their identities are not known.
The group also says fights broke out Friday in several contested areas of Aleppo and the Reef Dimashq and Hama provinces. None of the reports could be confirmed.
Kerry did not comment on the renewed reports of violence, but reiterated that the current situation cannot continue.
"There is no legitimacy in a regime that commits atrocities against its own people," Kerry said. "And we need to continue the work to make certain that the Assad regime makes a different set of choices."
Gallery of latest photos from Syria