Syrian tanks pounded residential neighbourhoods across the city of Hama today in the heaviest barrage of a two-day assault to crush street demonstrations against President Bashar al-Assad, witnesses said.

Earlier, residents said at least four civilians were killed by tank fire on the second day of attacks on the city, where memories are still vivid of the brutal suppression of an uprising in 1982.

Intense shelling began again after Ramadan evening prayers, concentrating on districts near the al-Bilal roundabout in the northwest of the city, the Jarajmeh district in the east and northern neighborhoods near the Omar bin al-Khattab mosque.

‘The shells are falling once every ten seconds,’ one witness said by phone.

At least 85 civilians have been reported killed in the crackdown on the central Syrian city, where Assad's father crushed an armed Muslim Brotherhood revolt 29 years ago by razing neighbourhoods and killing many thousands of people.

The European Union has extended sanctions against Syria as the country's army mounted another attack on the city of Hama, where more than 100 people are reported to have been killed yesterday.

The EU has frozen assets and imposed travel bans on five more people associated with the crackdown on opponents of President Assad.

The EU accused President Assad's forces of an indiscriminate massacre of civilians in Hama.

The United Nations Security Council is holding an emergency meeting today, at the request of Germany, to discuss the situation.

A spokesman for its UN mission said Germany had asked India, which holds the Council presidency for August, to schedule closed-door consultations and these were likely to take place in the afternoon, New York time.

President Barack Obama has denounced the attack on civilians and said he was appalled by the Syrian government's use of brutality against its own people.

The Syrian state news agency said the military entered Hama to purge armed groups that were terrorising citizens, an account dismissed as 'nonsense' by a US diplomat in Damascus.

The agency said eight police personnel were killed while 'confronting armed terrorist groups' in Hama.

Residents said tanks began pounding neighbourhoods of the city after attacking from several directions in a dawn assault.

Footage posted on social media showed large parts of the city covered in smoke, and panic-stricken groups surrounding the bodies of dead or wounded people in the streets as gunfire rang out.

The content could not be independently verified.

Britain and France condemned the Hama assault. Italy urged a tough statement by the UN Security Council, where Russia and China have previously opposed any condemnation of Syria.