LONDON, March 11 (Reuters) - Three foreign sailors kidnapped from their British-operated cargo ship by pirates last month off the coast of Nigeria have been released, the vessel's operator said on Monday.
There has been a surge in piracy attacks off the coast of Africa's most populous nation this year with gangs showing signs of moving further afield and using more violent tactics.
The British-flagged ship Esther C was boarded and ransacked on Feb.7, 80 miles (130 km) off the south coast of Nigeria by heavily armed pirates before they made off with the three seamen, Isle of Wight-based Carisbrooke Shipping said in a statement.
"The three officers were confirmed as being safe and in good spirits on March 11 after 31 days in captivity," it added.
A spokesman for Carisbrooke Shipping said separately the three crew members, two Russians including the ship's captain and a Romanian national, had been taken hostage and held in Nigeria before being released.
Armed gangs typically have targeted oil tankers and attacks on cargo ships are rarer.
Oil and shipping companies have to hire crisis management teams, pay higher insurance premiums and face the prospect of ransom payments, as well as brace themselves for damage to their reputations.
Oil majors Exxon Mobil and Shell said last month that security was a major factor in making Nigeria one of the most expensive oil-producing countries to operate in. (Reporting by Jonathan Saul; Editing by Michael Roddy)