BRUSSELS (Reuters) - The European Anti-Fraud Office (Olaf) said on Monday it was launching an investigation into claims by a newspaper that a senior trade official leaked commercially sensitive information in return for possible reward.

Olaf said it had "opened a case file" over an article by the Sunday Times accusing Fritz-Harald Wenig, a trade director, of passing information to undercover reporters posing as lobbyists for a Chinese businessman who wanted to know about secretive anti-dumping investigations.

The European Commission, the EU executive, has opened its own separate investigation.

When contacted regarding the case, a European Commission spokesman said the official in question was on annual leave. He was not immediately available for comment.

The Sunday Times said Wenig disclosed information about Chinese candle-making firms likely to be given lenient treatment in an anti-dumping case, and about other cases.

It said he discussed the possibility, proposed by the undercover reporters, of payment or working for the businessman.

But the newspaper also said the question of payment or a job was never decided and Wenig said he would do nothing illegal.

"OLAF recalls and fully respects the presumption of innocence of persons under investigation or subject to allegations under assessment," OLAF said in a statement.

If OLAF finds any wrongdoing, it will pass on its findings to the relevant national authorities which could lead to disciplinary or criminal proceedings.

The European Commission is responsible for investigating whether imports into the 27-nation EU are being "dumped" -- or sold at below their price in the home country or below cost.

The investigations are sensitive because they can lead to the imposition of anti-dumping duties on imports which affect the ability of companies to export to the EU's lucrative market of nearly 500 million consumers.