Russia is working to free seven of the 13 seafarers kidnapped off a tanker in the Gulf of Guinea last week.

The country's foreign minister, Maria Zakharova, confirmed on Monday that roughly half the seafarers taken off the 11,322-dwt Curacao Trader (built 2007) last Friday were Russian nationals, according to state-run news agency TASS.

"The Russian embassies in Abuja and Cotonou are constantly in contact with relevant Nigerian and Beninese agencies as well as representatives of the shipowner company. No efforts are spared to locate the kidnapped Russians and release them," Zakharova said.

"[The kidnappers] are yet to put forward any demands. On July 19, the ship anchored near the port of Cotonou."

According to Dryad Global, the Curacao Trader was 452 km south of Conotou when eight armed men boarded the ship. The maritime security consultancy said the attack was the furthest offshore pirate attack in the Gulf of Guinea to date.

Dryad had initially reported 15 seafarers of Russian and Ukrainian origin were kidnapped, but the ship's manager, Alison Management Corp, said it was 13 in a statement to TradeWinds on Saturday.

The company said its prime concern was the recovery of the crew "and no effort shall be spared to achieve their soonest possible release".

Dryad also said it dispatched the 8,097-dwt refrigerated cargo carrier Frio Chikuma (built 1998) to provide assistance.

Both the Frio Chikuma and the Curacao Trader are connected to the Laskaridis family.

Seafarers are held for an average of six weeks, according to the International Maritime Bureau, which tracks piracy.

The agency reported a total of 77 kidnappings in the first six months of 2020, a year-over-year increase from 75, with 49 taking place in the Gulf of Guinea.