* CFO, head of upstream detained
* Yara has faced several investigations
* Share drops more than 6 pct
OSLO, May 18 (Reuters) - Two senior executives at Yara , the world's largest maker of nitrate fertilisers, were charged on Friday in relation to an ongoing corruption probe.
Yara confirmed that charges have been filed by the Norwegian National Authority for Investigation and Prosecution of Economic and Environmental Crime, but declined further comment.
Norwegian police said they detained Chief Financial Officer Hallgeir Storvik and Head of Upstream Tor Holba on suspicion of "gross corruption," but would not say what the exact charges were.
"They were apprehended on suspicion of contribution to gross corruption," state prosecutor Marianne Djupesland of Norway's financial crimes police unit told Reuters.
"They are being held for the purpose of conducting separate interrogations. The aim is to obtain information that can confirm or disprove the suspicions."
Yara shares dropped sharply on the announcement and at 1354 GMT, they traded 6.6 percent lower at 233.4 crowns per share.
Yara has faced several police probes over the past two years in relation to its ventures or operations in Switzerland, Libya and India. (Reporting by Joacmin Dagenborg and Balazs Koranyi; Editing by Erica Billingham)