SINGAPORE (REUTERS) - Noble Group's chief executive has written to staff to say the Singapore-listed commodity trader's financials were improving and did not warrant Tuesday's "unexpected" move by Moody's Investors Service to downgrade its credit rating to junk status.

"We clearly feel this decision does not reflect the positive ratings impact of the recent Noble Agri (NAL) deal, but rather follows on from their recent lowering of ratings across the entire commodity sector," Yusuf Alireza said in a letter to employees following the downgrade.

"It seems that Moody's credit committee were not able to differentiate between an environment that is clearly challenging for upstream players and one that opens up opportunities for an asset light trader like ourselves," Mr Alireza said in the letter, which was reviewed by Reuters.

Asked to comment, a spokeswoman for Noble referred Reuters to a media statement in which the company said it has investment grade status with two other ratings agencies, and will work with Moody's to ensure that Noble's rating reflects the financial metrics that the company will attain.