Witnesses said police were guarding the buildings in Lagos and were not allowing people to enter. Telephone calls to all three offices went unanswered.
Military ruler General Sani Abacha announced on Wednesday that his government was dissolving the executives of Nupeng and its sister oil union Pengassan, as well as those of the umbrella Nigeria Labour Congress. He said administrators would be appointed to run the affairs of the organisations.
A six-week-old strike by the two oil unions, to press for the release of detained opposition politician Moshood Abiola, has disrupted domestic fuel supplies and led to cuts in crude oil production, Nigeria's main source of foreign exchange earnings.
The country has been in turmoil since June last year, when the regime annulled a presidential election, apparently won by Chief Abiola, which was supposed to end a decade of military rule.
In London, a Foreign Office spokesman condemned the crackdown on the unions as regressive and unhelpful.
'We had already made clear our view that the trial of Chief Abiola, the close of newspapers and political arrests could not help the current political crisis,' he said. 'The banning of trade union leadership . . . was a further regressive act that will not help the situation.'
He said these events only served to underline the need for more constructive efforts by the regime to engage all sides in political dialogue and resolve the crisis.