Syria has accused the US of incitement by sending its ambassador to the city of Hama without clearance from authorities in Damascus.

The foreign ministry in Syria has said that 'the presence of the US ambassador in Hama, without prior permission from the Foreign Ministry ... is a clear evidence of the US' involvement in current events in Syria and its attempt to incite an escalation in the situation, which disturbs Syria's security and stability.'

The US state department has said that Ambasador Robert Ford toured Hama to show solidarity with residents facing a security crackdown after weeks of escalating demonstrations against President Bashar al-Assad.

The State Department said that the US embassy had informed the Syrian government that an embassy team, without naming Ford, was travelling to the city, which residents say is still ringed with tanks.

The department has said that it has said he hoped to stay in the city until Friday, when more protests are planned.

Earlier, United Nations chief Ban Ki-moon has called on Syria to give UN aid workers immediate access to evaluate the needs of civilians caught up in a bloody crackdown on anti-government protests.

The world body has been largely shut out from Syria.

The country has also prevented most independent media from operating inside Syria, making it difficult to verify accounts from authorities and activists.

Mr Ban urged the government of President Bashar al-Assad to allow a team of UN human rights investigators, who have been in the region, to carry out their mission in Syria.

'In Syria, the killings continue and this must stop. I call on the Syrian leadership to deliver on its commitments and allow in the United Nations humanitarian assessment team and the human rights fact-finding mission mandated by the Human Rights Council. It is time to see progress there,' Mr Ban told reporters.

Residents in the Syrian city of Hama blocked streets with burning tyres today to keep out busloads of security forces, and dozens of families fled to a nearby town, an activist and a resident said.