Platiyali, Greece ? A rusting cargo ship was placed under heavy guard Monday as officials struggled to unravel its last voyage: Were hundreds of tons of explosives below decks linked to terrorism or simply a business deal gone bad?

The Greek coast guard impounded the Baltic Sky, and army demolition experts secured its cargo of 750 tons of industrial-grade explosives and 8,000 detonators that documents say were bound for Sudan.

The vessel was forced to anchor Sunday at an obscure Greek port after wandering the Mediterranean Sea for nearly six weeks — much of it under international surveillance.

Its crew — five Ukrainians and two Azerbaijanis — face charges that include entering Greek waters without announcing their hazardous cargo — ANFO, an explosive often used in mining and construction.

“It should have declared that it was sailing with a cargo that was like an atomic bomb,” Merchant Marine Minister Giorgos Anomeritis said.

The inquiry is complicated by the murky world of shipping, where the true owners of a ship often hide behind offshore management companies and vessels fly so-called “flags of convenience.”

Greek officials say the 1,717-ton ship is registered to Alpha Shipping Inc. based in the Pacific Ocean nation of the Marshall Islands.

Its flag, however, comes from the Comoros Islands, a nation off the southeast coast of Africa that is used by shipping companies as a flag of convenience to avoid taxes and regulations.

According to Anomeritis, the ship was boarded as part of the international war on terror. Greece and other nations had tracked the ship for weeks, he said.

Although the explosives were commercially made and packed in pallets, homemade versions of ammonium nitrate bombs have been the explosive of choice in many terrorist attacks — from 1995 in Oklahoma City to last year’s Bali bombings.

Used as a fertilizer, ammonium nitrate is harmless. But when mixed with fuel oil, it becomes an explosive more powerful than dynamite.