* Russian, 2 Indians, 3 Ukrainians kidnapped in attack
* Piracy off Nigeria coast is worsening
* Five attacks this month off Africa's top oil producer (Adds kidnap, details, background)
By Joe Brock
ABUJA, Feb 19 (Reuters) - Pirates kidnapped six foreign sailors when they boarded a ship two days ago off Nigeria's coast in the latest in a string of attacks off Africa's biggest energy producer, security sources said on Tuesday.
A Russian, three Ukrainian and two Indian sailors were taken when the Armada Tuah was attacked around 40 miles off the coast of oil-producing Bayelsa state, three security sources told Reuters. There were no details on what type of ship it was or where it was flagged.
Piracy off the Nigerian coast and elsewhere in the Gulf of Guinea is on the rise. There have been at least five attacks in the waters off Africa's most populous nation this month.
"If confirmed, the attack would be the third offshore kidnapping in the area in 10 days, following the attacks on Esther C and Walvis 7 on Feb. 7 and Feb. 10 respectively," Maritime risk experts AKE said in a security report.
Piracy watchdog the International Maritime Bureau (IMB) also confirmed the ship was attacked. The Nigerian navy did not respond to requests for comment.
Five Indian sailors who were kidnapped in a pirate attack around 40 miles off the Niger Delta coast in December were released last month. There were no details on how they were freed but in the past ransoms have been paid.
In a separate attack on Sunday, robbers in a wooden boat boarded a ship anchored at the Lagos port and stole the stores kept on the ship before escaping, the IMB said.
Suspected Nigeria pirates hijacked a French-owned Luxembourg-flagged tanker along with its 17-member crew off Ivory Coast this month, in a sign criminal gangs are spreading beyond traditional waters.
The Gulf of Guinea coastline, rich in natural resources such as cocoa and metals, is second only to the waters off Somalia for the risk of pirate attacks, which drives up shipping and oil industry costs.
Nigeria is near a busy oil shipping route. The West African country is among the world's top 10 crude oil exporters and imports around 80 percent of the fuel products needed for its 160 million people due to a lack of domestic refining capacity. (Additional reporting by Jonathan Saul in London; Editing by Jason Webb)