Syria accused the United States of meddling after the US ambassador visited the flashpoint city of Hama, where hundreds have fled fearing a crackdown ahead of anti-regime demonstrations on Friday.

Despite the U.S. State Department insisting Mr Ford's visit was to show solidarity with protesters, reports incriminating the U.S. rapidly emerged in the media, with some news agencies even reporting that the ambassador had come to hold talks with the opposition.

US State Department spokeswoman Victoria Nuland said Washington was "greatly concerned about the situation in Hama".

"The fundamental intention (of Mr Ford's visit) was to make absolutely clear with his physical presence that we stand with those Syrians who are expressing their right to speak for change," she said.

The Syrian foreign ministry has however counter attacked on Thursday and addressed a stiff warning to the U.S. by saying the visit by Robert Ford was "obvious proof" of US attempt to "increase tension and damage Syria's security and stability."

"The presence of the U.S. ambassador in Hama without previous permission is obvious proof of the implication of the United States in the on-going events, and of their attempts to increase (tensions), which damage Syria's security and stability," the foreign ministry said in a statement.

"Syria warns against such irresponsible behaviour and stresses its determination to continue to take all measures that will bring back calm and stability to the country," it added after Robert Ford's visit.

According to activists, fearing a brutal crackdown from the government's forces, hundreds of people have fled Hama ahead of planned demonstrations Friday and have instead headed to Salamiyah, some 30 kilometres (18 miles) to the southeast.

The protests will take place under the banner of "no to dialogue" with President Bashar al-Assad's regime, as one of the main demands is still the departure of the president and his government.

Throughout the week, Syrian authorities have been trying to quash protests in Hama which traditionally represent the centre of the opposition to the central government, by positioning tanks on the main entrances of the city, except in the north.

Despite the Assad regime still claiming that all is well and under control, the Syrian Observatory for Human Rights said that about 1,000 people in total had left Hama, before adding that Syrian troops had killed 25 civilians since Tuesday.

Observatory chief Rami Abdel Rahman said two civilians were killed on Thursday alone at Hama.

"Security forces shot them in the legs and then ran them over in their vehicle. They were fatally injured and died on the way to hospital," he said.

Hama has been a symbol of opposition since the 1982 crackdown on a revolt by the banned Muslim Brotherhood against then-president Hafez al-Assad, father of the present leader, in which some 20,000 people were killed.

On the other hand, Al-Watan newspaper, which is close to the regime, said the situation in Hama was calm and that the authorities had told demonstrators to avoid any confrontations and clear the streets so residents could go to work and to avoid what it called a "last resort" military operation.

But reports emerging from rights group and activists keep on contradicting the newspaper's allegations and insist that last Friday, an anti-regime rally brought out half a million people in the city.

However, they also reveal that after the security services did not intervene, Assad fired the city's governor the next day.

"Dialogue makes no sense if security forces do not pull out of the streets and the regime does not stop its violence against citizens," lawyer Anwar al-Bunni told AFP.

Rights groups say that more than 1,300 civilians have been killed and 10,000 people arrested by security forces since mid-March when the anti-government protests erupted.

UN chief Ban Ki-moon called on the Syrian president to make good on his promises.

"In Syria, meanwhile, the killing continues. This must stop," Ban said in Geneva.

"I call on the Syrian leadership to deliver on its commitments and to allow our UN humanitarian assessment team and the human rights fact-finding mission mandated by the Human Rights Council in.

"It's time to see progress here. We cannot go on like this."

The Obama administration has been criticised by many rights groups and activists for failing to take a stronger stance against the Assad regime, and despite Hillary Clinton's several warning to the Syrian regime, not much has been done to stop Assad from continuing to kill the citizens.

However the visit of Mr Ford, without permission with the Syrian authorities could increase Assad's suspicions that a coup is underway, which could push him to react even more brutally to the protests.