Nigeria's oil output was cut by around half on Monday after Exxon Mobil said all of its oil production in the country has been shut due to a workers' strike, while recent attacks by Niger Delta rebels affected Royal Dutch Shell output.

Around a dozen of workers of Exxon Mobile Corp.'s local affiliate stayed away from work for the third day as the employees' union and the company remained continue to disagree on issues including worker's pay.

The Nigerian government said it will try to mediate the dispute, but little progress has yet to be made.

The problems in Nigeria helped push oil prices to a record high near $120 a barrel during trade today. Crude oil closed 23 cents higher at $118.75.

Exxon had shut down some 770,000 barrels per day, due to the five-day-old strike, equivalent to nearly 40 percent of output from the world's eighth largest oil exporter.

Essentially all production of ExxonMobil's affiliates in Nigeria has been shut in. The affiliates will not speculate about the length of the shut-in nor how long it will take to restart production, Exxon Mobil said in an emailed statement.

Exxon said its affiliates in Nigeria pumped about 800,000 barrels per day in 2007.

Nigeria's problems come amid a U.K. labor dispute that is set to force the shut-in of 700,000 barrels a day, or 40 percent, of the Britain's crude production.

Meanwhile, Royal Dutch Shell PLC said it was still investigating the extent of damage following a rebel attack late Thursday on one of its facilities. Another assault on a separate facility on Monday caused the company to shut 169,000 barrels a day. Nigeria already had about 500,000 barrels a day shuttered before the past week's unrest.