Packages sent to an Army Post Office (APO) number for U.S. troops in Saudi Arabia must be mailed today to arrive by Christmas, according to the Defense Department.

Friends and relatives unable to meet today's deadline may prefer to use an air letter, which can be mailed as late as Nov. 26, or an air parcel, which can be mailed as late as Nov. 16 and still arrive on time.

Mailing can be done at any neighborhood post office, at normal U.S. rates, the Pentagon said. If the APO number is not known, correspondents are advised to send the letter, package or parcel to the address of the person's military unit in the United States and it will be forwarded.

The Pentagon said anything sent must be able to withstand at least seven to 10 days of heat at 100 degrees. It said letters are not being opened by Saudi authorities but a small portion of parcel mail "is examined as a spot check."

Saudi rules forbid "material contrary to the Islamic religion," the Pentagon said, but that should not preclude religious material "for the personal use of U.S. service members such as single copies of Bibles" or religious holiday cards.