PORT HARCOURT/YENEGOA, Nigeria (Reuters) - Security forces have deployed in two cities in Nigeria's oil-producing Niger Delta in the past two days to disperse former militants protesting over the non-payment of amnesty allowances.

Activists say the government is not keeping the promises it made during an amnesty period earlier this year and that the region, which is home to Africa's biggest oil and gas industry, risks returning to violence.

More than half a dozen armoured vehicles and four truckloads of armed police deployed in the Amarata neighbourhood of Yenegoa, capital of Bayelsa state, on Wednesday to disperse former militants demanding stipends, a Reuters witness said.

The men said they were owed 300,000 naira each promised in return for laying down their weapons earlier this year, but that the government had failed to pay up.

Similar protests broke out in Warri, the main oil city in neighbouring Delta state, on Tuesday with scores of former fighters loyal to ex-militant leader Government Tompolo demonstrating outside the guest house where he is staying before they were dispersed by the security forces.

"The ex-militants are already feeling used and abandoned. Their allowances are not paid as and when due and they are blaming their leaders for their woes," said Akinaka Richard, head of Grassroots Initiative for Peace and Democracy, a rights group based in the main Niger Delta hub of Port Harcourt.

"The (former militant) leaders themselves are beginning to feel that the government wants to turn their boys against them. Some of the ex-militants feel betrayed by their leaders and the amnesty committee that rehabilitation camps were not provided."

Militant attacks on the oil industry in the vast wetlands region have prevented the OPEC member from pumping much above two thirds of its 3 million barrels per day (bpd) production capacity, costing it an estimated $1 billion a month.