LAGOS (Reuters) - Royal Dutch Shell said on Monday gas output from its joint venture in Nigeria's western Niger Delta recovered to its highest level in two years last week after it was able to repair damaged pipelines.

The Anglo-Dutch giant said its SPDC joint venture produced a total of 512 million cubic feet of gas on November 18, significantly above previous average production levels of around 300 million cubic feet per day.

"We are pleased that all the gas has been used for domestic power generation and manufacturing, as these are key sectors for national economic growth," SPDC Managing Director Mutiu Sunmonu said in a statement.

The output is from four gas plants -- Utorogu, Ughelli East, Sapele and Oben -- the last two of which had not been producing since late last year because of militant attacks on pipelines.

An amnesty programme which offered militants in the Niger Delta a presidential pardon in return for handing over weapons has brought a period of relative stability in the region, with no attacks reported on energy infrastructure for several months.

Security experts warn the peace is fragile and that the gunmen may return to violence if they are not quickly retrained and found work.

Overhauling Nigeria's shambolic power sector has been one of the priorities of President Umaru Yar'Adua's two-and-a-half year old administration. Erratic power supply is one of the main brakes on growth in sub-Saharan Africa's number two economy.