Somali pirates also captured a German container vessel in the region's busy commercial shipping lanes on Saturday.
Mwangura said the 20,000-tonne Hansa Stavanger was seized 650km off the southern Somali port of Kismayu, between the Seychelles and Kenya.
"We believe the German ship has 24 crew on board. We're trying to establish their identities and the name of the vessel," he said.
Heavily armed gangs from the Horn of Africa nation have hijacked dozens of vessels in the past year, taking hundreds of sailors hostage and making millions of dollars in ransom.
Foreign navies have deployed warships to areas of the Indian Ocean in response to the piracy, reducing the number of successful attacks in recent months, but there are still near-daily attempts.
Seychelles deployed security forces on its outer island last week, after pirates hijacked a vessel flying the Indian Ocean nation's flag.
|Foreign navies have deployed warships to the area to tackle piracy [AFP]
Somali pirates typically use speed boats launched from "motherships".
They then take captured vessels to remote coastal village bases in Somalia, where the hostages are usually treated well in anticipation of a sizeable ransom payment.
In January, a Somali group released the Sirius Star - a Saudi supertanker loaded with $100m worth of crude oil - and its 25 crew after $3m was parachuted onto its deck.
Last September, the pirates also grabbed world headlines by seizing a Ukrainian cargo ship carrying 33 Soviet-era T-72 tanks.
It was released in February, reportedly for a $3.2m ransom. The pirates say the arrival of high-tech foreign warships in the waters off their country has made their work more dangerous.
Last month, Somali pirates seized two European-owned tankers.