'Unidentified substance' sent to U.S. embassy

(CNN) - U.S. officials are testing an "unidentified substance" that was sent to the U.S. Embassy and Consulate in Pakistan last week, an embassy spokesman told CNN.

No staff members were sickened.

An envelope containing the substance arrived at the U.S. Consulate in the southern city of Karachi on Thursday, spokesman Lou Fintor said. The following day, the U.S. Embassy in Islamabad received an envelope containing an unknown matter, he said.

At no time did the consulate or the embassy close, and both will be open for business on Monday, he said.

When the envelopes were received, Fintor said the staff took precaution and followed appropriate procedures. He did not elaborate.

"We take this matter very seriously, hoax or not," Fintor said.