Syrian tanks have shelled the city of Hama after nightly Ramadan prayers, on the third day of an armoured assault to crush some of the largest street protests against President Bashar al-Assad in a five-month uprising.

The shelling concentrated on the eastern Rubaii and al-Hamidiya neighbourhoods, the Aleppo road in the north and the eastern Baath district, two residents said.

A crowd, which tried to rally in the central Alamein neighbourhood after prayers marking the end of the daytime fast, came under rifle fire by Assad's forces.

There were no immediate reports of casualties.

Rights campaigners earlier said five civilians were killed today as tanks thrust further into the central Syrian city of 700,000.

Earlier, US senators called on the Obama administration to impose tough new sanctions on Syria's energy sector as Washington sought to put muscle behind its demand that President Bashar al-Assad halt his lethal crackdown on unarmed protesters.

‘The United States should impose crippling sanctions in response to the murder of civilians by troops under the orders of President Assad,’ Senator Mark Kirk, a Republican, said in introducing legislation to target firms that invest in Syria's energy sector, purchase its oil or sell gasoline.

Mr Kirk was joined in sponsoring the bill by Democratic Senator Kirsten Gillibrand and independent Senator Joseph Lieberman, who said it was time to push for ‘a democratic transition that reflects the will of the Syrian people.’

As the US weighed its next steps to respond to Assad's escalating suppression of protests, US Secretary of State Hillary Clinton met with representatives of Syria's fledgling opposition who said the battered pro-democracy movement badly needed stronger US support.

‘We really need to see President Obama addressing the courage of the Syrian people,’ said Mohammad Alabdalla, one of the US-based activists who met Ms Clinton.

‘We want to hear it loudly and clearly that Assad has to step down.’

Mr Obama and Ms Clinton have said Mr Assad has lost legitimacy, but have stopped short of directly calling on him to leave office as they did Egypt's Hosni Mubarak and Libya's Muammar Gaddafi.

Meanwhile, the European Union added Syrian Defence Minister Ali Habib and several other security officials to a list of members of Mr Assad's government targeted by asset freezes and travel bans today.

Five officials were added to the sanctions list published in the EU's Official Journal, including Syria's head of internal security, and the head of intelligence in the town of Hama, which the EU says was the scene of an indiscriminate 'massacre' of civilians at the weekend.

The EU has already imposed sanctions on Mr Assad and 29 other individuals, three of them Iranian military commanders, and has also targeted military-linked firms associated with the suppression of dissent.

Following a briefing on Syria by Oscar Fernandez Taranco, deputy head of the UN political department, all 15 council members spoke but the body took no immediate action, postponing discussion until today, diplomats said.