"The investigation has now uncovered unacceptable payments from the company's joint venture in Switzerland," Yara said in a statement.
Company spokesman Esben Tuman said it was too early to say the exact amounts of the payments in question, when they were made and who benefited from them.
"It appears that they were made over a long period of time and that they were for significant amounts," was all he would tell AFP.
The company said that the Norwegian economic crime unit had been informed of the finding.
The Norwegian company, one of the world's biggest mineral fertiliser producers, asked last year for an external investigation after discovering possible financial misdeeds committed before October 2008 in connection with the creation of its Lifeco joint venture in Libya.
The probe, which has been widened to all of Yara's operations outside Norway, has also uncovered suspicious payments in India linked to another joint venture project a few years ago, which in the end did not materialise.
The matter has already led Norwegian police to press charges against the company for "aggravated corruption."