The Pengassan union of oil workers had said last week that a strike over a pay dispute could have a "biting effect" on oil exports.

But the Nigerian government and oil company officials said on Monday the strike had not affected exports.

The Nigerian Department of Petroleum Resources (DPR) said it had sent staff to export terminals to carry out the supervisory role of its white-collar union members.

World oil prices are at two-year highs, amid fears of the impact of a war in Iraq on global crude oil supplies.

An oil workers' strike in Nigeria could have disrupted oil prices.

With exports of about 2 million barrels of crude oil per day, Nigeria is one of the world's biggest oil exporters.

A third of Nigeria's oil production goes to the US, where fuel heating reserves have been severely affected following the loss of Venezuelan supply after a crippling strike in the Latin American country.

Disagreement

On Monday, the Nigerian Government seemed to be in disagreement with the union over whether workers were actually on strike.

A spokesman for Nigeria's Ministry of Petroleum Resources said: "They are not going on strike as [of] the moment. I think they are going to hold some discussions."

But the secretary general of the Pengassan union, Kenneth Narebor, said some workers at the oil companies' administrative headquarters had walked out.

"From the reports I have now, it's started," Mr Narebor said.

Meanwhile, officials at oil giants Royal Dutch/Shell, ExxonMobil and the Nigerian National Petroleum Corporation said their operations were not affected.

A spokesman for US oil company ChevronTexaco said that production had not been disrupted although some workers had walked out.

'No official records'

Nr Narebor said crude oil exports would definitely be affected by the strike.

A Pengassan union leader said on Sunday exports were likely to continue because oil companies use their own staff at tanker terminals.

"Exports can go on, but the government will be the ultimate loser because Pengassan members will not be there to ascertain the quantity and quality of exports," Paul Ekele, DPR Pengassan branch chairman said.

"There will be no official records to collaborate the claims of the oil companies."

The Petroleum and Natural Gas Senior Staff Association of Nigeria, or Pengassan, called the strike on Saturday after talks with government over pay arrears and autonomy had failed to produce any results.