* Energy facility attacks in 2016 slashed oil production
* Niger Delta Avengers warn of bloody campaign
* Group says lost faith in local leaders
* Nigeria left recession in second quarter of 2017 (Adds details, quotes, bullet points)
LAGOS, Nov 3 (Reuters) - A Nigerian militant group whose attacks on energy facilities in the Niger Delta last year helped push Africa's biggest economy into recession said on Friday it had ended its ceasefire.
The Niger Delta Avengers announced a halt to hostilities in August 2016, although they carried out attacks in October and November last year.
The 2016 attacks cut oil production from a peak of 2.2 million barrels per day (mbpd) to near 1 mbpd, the lowest level in Africa's top oil producer for at least 30 years.
The attacks, combined with low oil prices, caused the OPEC member's first recession in 25 years. Crude sales make up two-thirds of government revenue and most of its foreign exchange. Nigeria came out of recession in the second quarter of this year, mostly due to the rise in oil production after attacks stopped and as prices strengthened.
"Niger Delta Avenger's ceasefire on Operation Red Economy is officially over," the group said on its website ( http://www.nigerdeltaavengers.org/ ).
"Our next line of operation will not be like the 2016 campaign which we operated successfully without any casualties; this outing will be brutish, brutal and bloody," it said in a section of its statement addressed to oil companies.
The move threatens Nigeria's fragile economic growth and poses a further security challenge for President Muhammadu Buhari, in addition to the jihadist Boko Haram insurgency in the northeast and rising secessionist sentiments in the southeast.
The government has been in talks for more than a year to address grievances over poverty and oil pollution but local groups have complained that no progress has been made, despite Buhari receiving a list of demands at a meeting last November.
The Niger Delta Avengers, who say they want a greater share of Nigeria's energy wealth to go to the impoverished swampland region, said they decided to end the ceasefire because they had "lost faith" in local leaders.
"We can assure you that every oil installation in our region will feel the warmth of the wrath of the Niger Delta Avengers," it said.
There have been no substantial attacks in the region since January.
Nigeria's economy grew 0.55 percent year-on-year in the second quarter, largely on higher oil receipts.
The World Bank cut its 2017 growth forecast in October to 1 percent from 1.2 percent as the oil production increase was lower than expected and non-oil sector growth was subdued. (Additional reporting by Libby George in Abuja and Christopher Johnson in London; Editing by Kevin Liffey and Robin Pomeroy)