By Felix Onuah

ABUJA (Reuters) - The Nigerian government is talking to militants in the Niger Delta to end a wave of attacks on oil and gas facilities which have cut oil production by 700,000 barrels a day, top officials said on Thursday.

But the Niger Delta Avengers, a militant group that has claimed responsibility for a series of attacks, said it was not aware of any talks, saying there would be no dialogue without involving the international community

The government was using oil companies and security agencies to talk to the militants "to find a lasting solution to insecurity in the region", President Muhammadu Buhari said in a statement.

Buhari also said his government was reviewing an amnesty program for former militants, which offers cash and job training, after initially slashing the scheme's budget by two-thirds and angering militants.

"We understand their feelings," Buhari said. "We are studying the instruments (of the amnesty). We have to secure the environment, otherwise investment will not come."

In June, government officials said a one-month ceasefire had been agreed with the Niger Delta Avengers but the group reiterated on Thursday no talks were going on.

"We are not aware of any peace talk," the group said in a statement on its website. "President Buhari... is not sincere to the Nigeria people and their foreign allies."

Militants say they want a greater share of Nigeria's oil wealth to go to the impoverished Delta region. Crude sales make up about 70 percent of national income and the vast majority of that oil comes from the southern swampland.

Nigeria, an OPEC member, was Africa's top oil producer until the recent spate of attacks pushed it behind Angola.

Pipeline vandalism has reduced oil production by 700,000 barrels a day, Maikanti Baru, the new managing director of state oil firm NNPC, said in a statement.

"The 2016 national budget plan was based on 2.2 million barrels per day of crude oil production," Baru said. "However, the budget plan is now grossly impacted due to renewed militancy: with about 700,000 bpd of oil production curtailed due to pipeline vandalism."

"Domestic natural gas supply to power is equally impacted with (an) estimated drop of about 50 percent from 1,400 million standard cubic feet of gas per day," he said.

(Reporting by Felix Onuah; additionalk reporting by Parikshit Mishra; Writing by Ulf Laessing; Editing by Angus MacSwan)