OTTAWA -- The U.S. Embassy in Ottawa called police yesterday after receiving an envelope containing a suspicious white powder that was addressed to Ambassador Kelly Craft.

An embassy spokesperson says the letter was discovered by staff at an off-site mail-screening facility.

The spokesperson says tests on the substance found that it was not harmful.

The U.S. embassy is declining to provide further details about what else was in the envelope because of an ongoing investigation into the incident.

The spokesperson says the envelope was addressed to Craft at the address of the U.S. Embassy -- but won't confirm whether the letter contained threats.

The incident involving U.S. President Donald Trump's envoy to Canada comes amid heightened tensions between the two countries that has resulted in stalled trade talks, the imposition of tariffs and even a public, personal attack directed at Prime Minister Justin Trudeau by Trump and his senior officials.