WASHINGTON (Reuters) - The United States remains on alert against the possibility of new terror attacks, Homeland Security Director Tom Ridge said on Wednesday.

Ridge told reporters at the White House that there was "no change" in the security warning put out on Oct. 29 by Attorney General John Ashcroft.

"We're still on alert," Ridge said. "We will be on alert indefinitely. And when we have specific information from credible sources we will appropriately give it to the law enforcement community."

He said there was no specific place believed to be the target of a possible attack nor did officials know when it might take place.

The issuance of the general threat, the second such alert issued since the Sept. 11 attacks, has created some confusion among Americans as to how to respond because they are also being told by the government to go on with their normal lives.

Ridge also said federal investigators remained baffled as to the source of anthrax in the United States that has killed four people and triggered an anthrax scare in parts of the country.

"We haven't included or excluded either a domestic or an international source for the anthrax. There have been some suggestions that it could be domestic, but that has not been confirmed in any manner, shape or form," Ridge said.

But with no new anthrax cases reported in the last week, Ridge said the crisis may be over although authorities continued to deal with traces of the deadly bacteria found in Washington and New Jersey.

"I am hopeful, like the rest of America, that the anthrax has stopped permanently," Ridge said. "We certainly haven't seen or detected any new sources of anthrax."

Ridge said he conferred on Tuesday with Sir Christopher Meyer, the British ambassador to the United States, about how Britain has dealt with the Irish Republican Army in Northern Ireland.

"This is a country that unfortunately has had a real-world experience with political terrorism of different sorts; and he brought some of the security people in," Ridge said.

"We will be putting together a team to sit down with him and with other members of our international coalition that are helping us on the war in Afghanistan," he said.