Israel suspended postal deliveries nationwide on Monday after a letter bomb was found in a post office, police and postal authorities said.

The motive behind the mailing of the explosives was not immediately clear, a police spokesman said, and a court imposed a gag order in the investigation.

The letter bomb was found in a post office in the northern town of Migdal Haemek, where a woman spotted wires and batteries in an envelope she had come to collect.

A police spokesman said police were investigating whether the incident was a local criminal event or not.

After the discovery, Israeli authorities took the rare step of stopping the mail service nationwide pending a thorough search of mail at the country's main postal distribution centres where they are sorted for delivery, postal officials said.

"We are not distributing any mail at the moment nor taking in any mail because we want to protect public safety," Avi Hochman, director of Israel Postal Services said on Army Radio.

Reuters