Syria has condemned a visit by United States Ambassador Robert Ford to the key opposition city of Hama, accusing the U.S. of attempting to incite anti-government sentiment ahead of more protests planned for Friday.

The Syrian foreign ministry said Thursday that Ford's presence in Hama without prior permission constitutes “clear evidence” of a U.S. attempt to “increase tension and damage Syria's security and stability.”

In Washington, State Department spokeswoman Victoria Nuland said Ford met with a dozen people in a visit designed to show solidarity with protesters. She said Ford hopes to stay until Friday and that the U.S. embassy had informed the Syrian government that an embassy team was travelling to the city.

Earlier, a Syrian activist monitoring developments in Hama told VOA in a telephone interview that dozens of families fled the city Thursday fearing a military crackdown. She said security forces have surrounded Hama with tanks, and that troops have detained more than 100 people.

The activist confirmed reports from rights groups that at least 25 people have been killed and more than 40 wounded in Hama in recent days. Troops had pushed through improvised barriers and roadblocks set up by Hama residents after massive anti-government protests last week.

United Nations Secretary-General Ban Ki-moon urged Syria to stop its deadly crackdown on dissent. Mr. Ban also asked the Syrian leadership to grant access in the country to U.N. aid workers and a fact-finding mission.

Rights groups say Syrian security forces have killed at least 1,400 civilians since mid-March while trying to suppress the anti-government uprising. The Syrian government says terrorists and Islamist militants have killed hundreds of security personnel during the same period.

Amnesty International said Syrian forces may have committed crimes against humanity during an operation last month near the Lebanese border.

The London-based rights group Wednesday accused Syria of rounding up scores of male residents in the town of Talkalakh and torturing most of them. It quotes witnesses who say at least nine people died in custody.