VIENNA, March 29 (Reuters) - The United States has identified the remains of an Austrian security guard kidnapped in Iraq in 2006 with four American colleagues, the Austrian government said on Saturday.

"The agony of uncertainty of the past one and a half years has given way to sad certainty. Bert Nussbaumer is dead. Our worst fears have become true," Austrian Foreign Minister Ursula Plassnik said in a statement.

The U.S. Federal Bureau of Investigation notified Nussbaumer's relatives late on Friday that DNA tests on one of five sets of remains recently recovered in Iraq showed they were those of the 26-year-old Austrian, a ministry spokesman said.

His remains will be returned to Austria shortly.

Earlier this week the FBI confirmed the deaths of Americans Paul Christopher Johnson-Reuben, Joshua Mark Munns and John Roy Young. They and Nussbaumer were working for the U.S. Crescent Security Group when snatched near Basra in November 2006.

The remains of another U.S. security guard kidnapped in the chaotic area in January 2007, Ronald Withrow, who worked for JPI Worldwide, were also identified on Monday.

A fifth Crescent guard abducted in November 2006 remains unaccounted for.

Plassnik said the kidnappers had not communicated any demands or conditions for the release of Nussbaumer. His mother, Maria Nussbaumer, was quoted by Austrian daily Oesterreich as saying she was "disappointed and enraged" because she felt Washington had never mounted a serious effort to get the missing contractors freed. (Reporting by Mark Heinrich; Editing by Robert Woodward)

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