But after tests showed that it was apparently flour or food based, the powder was declared harmless. Earlier on Thursday, some offices of the newspaper were evacuated as a precautionary measure.

"There were at least a dozen envelopes that we know of," a spokesman for the paper said but declined to name to whom they were addressed.

But the New York Times, citing the WSJ employees, said that at least some envelopes were sent to the managing editor Robert Thomson, the editorial page editor Paul A. Gigot, and the chief executive of Dow Jones and Company Leslie Hinton.

"It appears that the individual or individuals took the masthead of The Wall Street Journal and just wrote down those names," a police spokesman said.

The official put the total number of envelopes, with the addresses typewritten, at 10 to 12.

In all, three envelopes were opened, the spokesman said, adding each contained the white powder and a blank piece of paper. The letters were postmarked from Knoxville, Tennessee but return addresses were different.

The Times said a letter with similar markings, also postmarked from Tennessee, was received on Wednesday at Harvard Law School and was addressed to legal scholar Alan M Dershowitz.

It quoted police as saying that Wednesday's incidents may be linked to similar mailings of white powder to the Fox News Channel and to several conservative commentators in early December, 2008.