Nigeria's main oil workers' union has announced an indefinite strike that could cripple the country's crude oil exports.

Nigeria is the world's seventh largest oil exporter and the strike, which union organisers say will start to bite on Monday, is likely to push prices higher in the international marketplace.

It is going to be an indefinite strike, but we appeal to Nigerian international partners to bear with us Bayo Olowoshile, Pengassan union

The news may alarm oil importing countries which are already facing high prices and the prospect of supply disruptions from the Middle East.

On Friday in New York the price of US crude oil reached its highest level for nearly two and a half years. It was up 44 cents at $36.80 a barrel.

In London the benchmark Brent crude closed 4 cents higher at $32.50 a barrel.

Members of Nigeria's Pengassan union will walk out on Saturday in a dispute about pay.

The action will involve employees of the state-run Department of Petroleum Resources (DPR) who supervise the loading of oil at export terminals.

Joint ventures

"We shall, by this strike, force a dialogue from government on the demands of our members," said the union's deputy general secretary Bayo Olowoshile.

Those members are asking for a pay rise and pay arrears.

Pengassan officials said the union had received a letter from the government on Friday proposing a meeting on 25 February, but they said this would be far too late.

"There is no sign to show that things can change," said Mr Olowoshile.

"It is going to be an indefinite strike, but we appeal to Nigerian international partners to bear with us."

Nigeria has joint venture partnerships with oil groups including Shell, ChevronTexaco, ExxonMobil and TotalElfFina.

Pressure on prices

Industry analysts say Nigeria will lose millions of dollars in oil revenue if the strike goes ahead.

The country sends more than two million barrels a day abroad.

More than half of its exports go to the US.

US fuel reserves are already at record lows because its imports have been affected by a two-month long strike in Venezuela.