Syria's opposition has won fresh financial and material support from the US but its demands for weapons to fight Bashar al-Assad were ignored in favour of calls for a "political solution" to end the crisis.

John Kerry, the new US secretary of state, announced at a conference in Rome on Thursday that $60m (£45m) in "non-lethal" assistance would go to the western-backed Syrian National Coalition (SNC) while food and medical supplies would – for the first time – go directly to the opposition's supreme military council, attempting to co-ordinate strategy by the Free Syrian Army and other units.

"Assad cannot shoot his way out of this," Kerry said after a meeting of the Friends of the Syrian People group. "And as he deludes himself on a military solution, [we] make a different choice. Our choice is a political solution."

But Moaz al-Khatib, the president of the SNC, protested openly at what he called "an international decision to prevent arming Syrian rebels with quality arms."

Rumours that the US might supply body armour, military vehicles or communications equipment or training did not materialise. It is now public knowledge that Barack Obama blocked a proposal by the CIA and Pentagon to arm the rebels last year.

Khatib, a former imam of the Umayyad mosque in Damascus, also scorned western concerns about the increasing prominence of fundamentalist or jihadi groups in the anti-Assad camp. "Plenty of people focus more on the length of a fighter's beard than on the scope of the regime's massacres," he complained.

Last December the US declared Jabhat al-Nusra, a fighting group with jihadi/al-Qaida links, a terrorist organisation.

Khatib, who caused controversy recently when he called publicly for negotiations for an end to the Assad regime, insisted again that it had to go and its security agencies had to be dismantled.

"Bashar al-Assad, you have to behave as a human being for once in your life," he urged. "Enough killing, enough slaughtering, enough arresting. Bashar, you need to make one reasonable decision in your lifetime to save this country."

He also called for an end to arms supplies to the regime – a clear reference to Russia and Iran, Assad's principal backers.

The SNC issued a statement calling on the Friends of Syria to act against the regime's "crimes" after the discovery of the bodies of 72 people it said had been executed by "Assad death squads" in Maalikiya village near Aleppo three days ago.

Khatib had intended to boycott the Rome conference because of anger that so little is being done by the west to help advance the anti-Assad cause. But he was persuaded to go by Kerry and Joe Biden, the US vice-president. Colleagues from the Syrian National Congress, the older opposition formation, still stayed away.

Against a background of escalating fighting in the Damascus area Kerry lambasted "the continued brutality of a superior armed force propped up by foreign fighters from Iran and Hezbollah, all of which threatens to destroy Syria".

The UN says 70,000 people have been killed in Syria over the past 23 months.

The new US funding is to allow the opposition to help local councils provide medical care, food sanitation and basic services in liberated areas. "Syrians who share our values need to demonstrate that they can deliver a better day and need to set an example of a Syria where daily life is governed neither by the brutality of the Assad regime, nor by the agenda of al-Qaida-affiliated extremists," said a senior state department official.

The new aid won only a qualified welcome from Syrians. "You need to dry up the source of the suffering rather than deal with the suffering after the fact," the opposition spokesman Saleh Mubarak told al-Jazeera TV. "Every day we wait for a solution, 150-200 civilians in Syria lose their lives."

Echoes of controversy over the crisis reached the Rome event when a journalist from the leftwing paper Il Manifesto disrupted Kerry and Khatib's speeches by waving a banner reading: "USA, EU, Italy, Turkey, Qatar support terrorists."

Differences between western and Arab countries were underlined in comments by the Saudi foreign minister, Saud al-Faisal, who said Europe should be arming the rebels. The kingdom was giving "all the support it can", he said.

Britain's foreign secretary, William Hague, spoke of determination 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. But support will still be carefully calibrated because of the continuing hope in Washington, London and other western capitals for Russian pressure on Assad to negotiate an end to the crisis rather than fight to the bitter end.

The Russian president, Vladimir Putin, said his country and France agreed that Syria must not be allowed to break up. "Despite the existing differences in the Russian and French positions we are for keeping Syria an integral, democratic state," Putin told a joint news conference after talks with the French president, François Hollande.

"We must go above and beyond the efforts we are making now," said the Italian foreign minister, Giulio Terzi, who hosted the conference. "We can no longer allow this massacre to continue."