Egyptian navy forces seized a ship carrying heavy weapons as it entered Egyptian territorial waters in the Red Sea, a military spokesman said.
The Togolese-flagged ship, called COMR, was found 12 nautical miles north of Ras Muhammad in the Sinai Peninsula, general staff spokesman Ahmed Mohamed Ali said on his Facebook page.
"Inside they found a number of weapons and quantities of ammunition of various types," Ali said.
"The boat belongs to a private maritime security company which serves to secure ships passing through highly dangerous areas, especially in light of the spread of piracy in the southern Red Sea area and off the Somali coast," he added.
Security sources told Reuters earlier that the ship, with a crew of at least seven, spent a week in international waters before entering Egyptian waters.
The vessel was escorted into the port of Safaga, 569 kilometres southeast of Cairo, where the crew members were being questioned and an investigation was under way to determine whether the weapons were legal, the sources said.
"The weapons and ammunition seized in the vessel are linked to the nature of their work and the tasks assigned to them to secure commercial vessels," Ali said in his statement.
International shipping companies have begun to employ private security firms to ward off the threat of Somali pirates, with contractors often picking up weapons from ships off the coast of Djibouti as they enter the areas at risk.
That, together with the presence international warships patrolling the Indian Ocean, has seen the number of successful pirate seizures of ships fall sharply to five ships in 2012, from 25 in 2011, and 27 in 2010.