Nigerian troops have rescued 19 hostages kidnapped by militants¹ in the Niger Delta² this month, officials say.

官员称，尼日利亚军队已成功解救本月在尼日尔三角洲被激进分子劫持的19名人质。

Mend says it is fighting for fairer distribution of Nigeria's oil money

Two Americans, two Frenchmen, two Indonesians and a Canadian were freed along with 12 Nigerians in a land, air and sea assault（攻击，袭击） , said officials.

Security sources told the BBC the freed hostages were euphoric（精神愉快的） .

The operation was the first successful rescue of foreign captives in the Delta without any of the hostages being killed in the process.

It is not clear exactly where the operation was carried out, nor whether any militants were killed or wounded.

The foreigners were captured on 8 November, when gunmen attacked an oil rig belonging to London-based Alfren PLC.

The eight Nigerians were seized on an ExxonMobil platform in Akwa Ibom state a week later, in an attack claimed by Mend, a military group operating in the Delta.

Canada and France have both expressed their relief that the citizens are free and thanked the Nigerian authorities for their efforts.

The BBC's Caroline Duffield in Lagos says the rescue operation marks a change in tactics（策略，战术） by the Nigerian military, who worked in close co-operation with local contacts to free the captives.

Violence in the oil-rich Delta region has subsided³（平息，减弱） since last year.

In the past, militants have cut the country's oil production by one-third, causing a spike⁴ in global oil prices.

The government and many oil militants reached a ceasefire agreement last year in exchange for cash payouts and job training - but a small faction⁵（派别，内讧） of Mend has resumed the kidnappings.

There were always fears that a new generation of militants would emerge which would ignore the ceasefire, says our correspondent.

There are also signs the amnesty（大赦，特赦） is faltering⁶, following a firebombing attack on the home of presidential adviser⁷ Timi Alaibe last week, she adds.

Mend says it is fighting so that more of Nigeria's massive oil wealth is used to benefit the Niger Delta area which produces the oil.

But criminal gangs have taken advantage of the region's instability to make money from ransoms⁸（赎金） paid by oil companies, and stealing oil.