The US is to step up its support for the Syrian opposition as it fights to topple President Bashar al-Assad, Secretary of State John Kerry says.
Mr Kerry said the US would provide direct support to rebel forces in the form of medical and food supplies.
He also promised an additional $60m (£40m) in aid to the opposition to help it deliver basic governance and other services in rebel-controlled areas.
Mr Kerry was speaking at a gathering of the Friends of Syria group in Rome.
On Friday he is travelling to Ankara to discuss the Syria crisis with top Turkish officials.
'Out of time'
The promise of direct, non-lethal aid to the rebels represents a shift in US policy on Syria, correspondents say.
However it falls short of providing the weapons and munitions that the rebels say they need to defeat government forces.
Mr Kerry said the decision was designed to increase the pressure on President Assad to step down and allow a democratic transition.
"The US decision to take further steps now is the result of the brutality of superior armed force propped up by foreign fighters from Iran and Hezbollah.
"President Assad is out of time and must be out of power," said Mr Kerry, adding that the Syrian leader could not "shoot his way out" of the situation.
The $60m in aid to the opposition Syrian National Coalition (SNC) represents a doubling of US support.
It was intended to help the opposition deliver governance and basic services in rebel-controlled areas, said Mr Kerry.
"As the regime continues to lose ground it will help the opposition extend stability and build representative government and the rule of law," he added.
After the meeting, the European Union announced changes to its arms embargo on Syria, allowing EU states to provide armoured vehicles, non-lethal military equipment and technical aid to the rebels, but not weapons.
At the meeting with Mr Kerry, leader of the SNC, Moaz al-Khatib, said he was still frustrated by the lack of military help for rebel fighters.
He initially refused to attend the Rome talks in protest at a lack of international support for the Syrian rebels, but was persuaded after the US and UK indicated there would be specific promises of aid.
Speaking at the meeting Mr Khatib called on President Assad to make "one wise decision in your life" and stand down "for the future of your country".
Earlier this month he also suggested for the first time that talks with the Assad government might be possible, though that suggestion remains controversial among opposition groups.
The SNC says it plans to set up a government to administer rebel-held areas of Syria, primarily in the north of the country close to the Turkish border.
But a meeting to select the prime minister, scheduled for the weekend, was unexpectedly postponed on Thursday, and no new date has been set.
Meanwhile fighting in Syria continues and the humanitarian situation is worsening.
In the latest fighting, rebel forces have captured the historic Umayyad Mosque in Aleppo, according to an activist group.
The mosque was damaged and its museum caught fire as rebels forced government troops to withdraw, UK-based activist group the Syrian Observatory for Human Rights said.
Fighting also raged elsewhere in Aleppo's old city, including near the Palace of Justice, it added.
Aleppo - Syria's second city - has been a key battleground in the conflict.
Mr Kerry highlighted the fate of the city in his address, accusing President Assad of engaging in "ruthless attacks" with Scud missiles against rebel-held areas.
According to UN estimates, more than 70,000 people have been killed in Syria since the revolt against President Assad began nearly two years ago.
Opposition fighters have been constantly outgunned as President Assad's forces deploy tanks, aircraft and missiles against them.
The UN's refugees agency says the number of Syrians who have fled the conflict into neighbouring countries is now approaching one million, while two million have been internally displaced.
The World Health Organisation has warned of disease outbreaks and worsening medical services.
Earlier, UK Foreign Secretary William Hague said the Friends of Syria were determined to "ramp up" assistance to the opposition.
"We are entering a new phase in the response of Western and Arab nations to the crisis in Syria," he said.
The Friends of Syria organisation has broad international support, but does not include Syrian allies Russia and China.
On Thursday Russian President Vladimir Putin held talks on Syria with his French counterpart Francois Hollande.
He conceded that there were differences in the positions of Russia and France, but said both had agreed that Syria should not be allowed to break apart as a result of the conflict.