"The seven men have been arrested on suspicion of seizing or exercising control of a ship by use of threats or force," Hampshire Police said in a statement.

The stowaways were held after the Royal Navy's elite Special Boat Service (SBS) swooped on the Nave Andromeda on Sunday night, after it issued a mayday call near the Isle of Wight.

British media said police called in military assistance at about 5:00 pm (1700 GMT) on Sunday, and some 40 personnel were deployed to the scene, including snipers.

Some 16 SBS troopers with assault rifles and night-vision goggles fast-roped onto the deck of the 42,338-tonne tanker from two helicopters, securing the ship within nine minutes.

"BRAVO ZULU (well done) to the remarkable Armed Forces personnel involved," tweeted the highest ranking officer of the UK naval forces, First Sea Lord Admiral Tony Radakin.

Prime Minister Boris Johnson said the police and armed forces did a "fantastic job".

Hampshire Police said the stowaways, who are thought to have smuggled their way onto the Liberian-flagged vessel in Lagos, Nigeria, made threats to the crew.

"All 22 crew members are safe and well and the vessel is now alongside in the port of Southampton," the force said in a statement.

"Investigators are speaking to the crew members to establish the exact circumstances of what happened."

Law firm Tathan & Co., which represents the ship's Greek owners, had told the BBC the incident was "100 percent not a hijacking".

Instead, the stowaways resisted being locked in a cabin after being discovered, the lawyers said.

Crew members reportedly retreated to the ship's secure citadel for protection before alerting the authorities.

The SBS were previously deployed in December 2018 after four stowaways from Nigeria and Liberia threatened the crew of a an Italian cargo ship in the Thames estuary, east of London.

The four men were cleared of hijacking but jailed in January this year for various other offences, including affray and making threats to kill.

The Gulf of Guinea off southern Nigeria is a hotspot for maritime piracy, hijacking and abduction of crews, who are often taken back to the creeks of the Niger Delta.

They are usually released after a ransom is paid.