By BBC News Online's Kevin Anderson in Washington

After the most recent security alert in the US, a $7 million surveillance centre in Washington swung into action bringing together local and federal authorities to watch public sites for suspicious activity.

We have not done this under the cover of darkness

Washington Chief of Police Charles Ramsey

The centre brings in camera feeds from around Washington so that authorities can keep tabs on sites such as the Capitol, the White House and the Washington Monument.

Authorities say the new technology helps them better protect the city and its residents, allowing them to patrol more areas with fewer people.

But civil libertarians say that it is an invasion of privacy and violates the US Constitution.

Electronic eyes

Washington police began investigating such a system after the use of video camera surveillance during protests against the World Bank and International Monetary Fund over the last two years, said Washington Metropolitan Police Department Chief Charles Ramsey.

Authorities do not record any of the video feeds. The cameras have no microphones to pick up sounds or conversations, and Chief Ramsey said the cameras lack the resolution to allow authorities to identify individuals in a crowd.

The police department operates 20 cameras but can tap into many more around Washington

The system runs on a private wireless network similar to the technology that runs wireless networks in offices and, increasingly, in homes.

The cameras can pan 360 degrees and can zoom in up to 176 times. A camera mounted in Washington was able to see clearly the control tower of Ronald Reagan National Airport more than two miles away.

Right now the police department has 20 cameras of its own which can link to nearby cameras in the states of Maryland and Virginia.

At the heart of the system is the $7 million Joint Operations Command Centre.

The main feature of the room is some 20 large screens showing many of the landmarks of Washington.

The command centre has seats not only for Washington police, but also for some of the federal law enforcement agencies responsible for security in the nation's capital, including the Secret Service, the Coast Guard and the US Marshals.

It is only in operation during security alerts such as have been issued since the 11 September attacks.

Critics seek information

But the system has touched off protests from cyber civil libertarians.

The Electronic Privacy Information Centre (EPIC) has filed a legal request asking for information about the system.

Marc Rotenberg, the Executive Director of EPIC, said: "We are going to find out everything we can about this system: Who is the contractor? What is the cost? What data will be collected and who will have access to it?"

Union Station is one of the areas under surveillance for suspicious activity

He said in the past when the government has tried to expand state surveillance through the use of new technology, there has been a public outcry, and he said even after 11 September, the public is still concerned.

"We are still seeing in the US opposition to national identity cards, biometrics and face recognition," he said.

Washington's Union Station is one of the sites under surveillance, and some there expressed outrage.

"An invasion of privacy? I think it stinks, really. You should have some privacy," said one woman.

But another man said: "I don't think we have any expectation of privacy in such a public place. You have a million eyes on you anyway, why not some police eyes?"

Policies evolving

But Chief Ramsey said that critics who say the system amounts to the "Big Brother" of government violating the privacy of ordinary citizens "haven't bothered to see the room and haven't learned about it."

"The reality is that we're in the 21st Century, not the 18th," he said, adding that people face increased electronic monitoring in many areas of their lives and not always from governments.

He pointed to the cameras at ATMs and in stores, the discount cards from grocers which track purchases and record spending patterns, and pop-up ads on the internet that are based on the sites that web surfers visit.

But he said that authorities are aware of the privacy concerns and policy issues that remain unresolved and said that they had met the American Civil Liberties Union to seek their input.

"We have not done this under the cover of darkness," he said.