WASHINGTON (Reuters) - Security has been heightened in New York City because of a credible but uncorroborated threat, New York Mayor Michael Bloomberg said on Thursday, but said city residents should go about their business as usual.

"The NYPD (police department) is deploying additional resources around the city and taking additional steps to keep our city safe, some of which you may notice and some of which you will not notice," Bloomberg said at a news conference.

"But there's no reason for any of the rest of us to change anything in our daily routine."

Bloomberg said the threat has not been corroborated, but that it was credible and residents should be vigilant.

The White House said President Barack Obama was briefed on specific threat information earlier in the day, and noted that the government had already stepped up security ahead of the 10th anniversary of the September 11, 2001 attacks.

(Reporting by JoAnne Allen; editing by Todd Eastham)

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