The Angolan navy and air force is hunting suspected pirates after an oil tanker went missing in its waters.
Navy Captain Augusto Alfredo told the BBC that an unknown vessel had been seen near the Greek-owned 75,000 tonne MT Kerala as it lay off Luanda‚Äôs port.
But he said he could not confirm it was a pirate attack, which would be the first in the country‚Äôs waters.
Angola is one of the world‚Äôs biggest oil producers.
The oil mostly comes from off-shore rigs in the Atlantic Ocean.
There has been a huge surge in pirate attacks off Nigeria in recent years but never one so far south.
In contrast, piracy off the Somali coast has declined dramatically.
‚ÄúWe are concerned. Piracy is a phenomenon that concerns everyone as it poses a threat to any country,‚Äù Capt Alfredo told the BBC‚Äôs Focus on Africa radio programme.
‚ÄúWe will be taking measures to avoid a repetition. As you know, offshore oil production accounts for most of the Angolan domestic revenue,‚Äù he said.