Import prices recorded their largest decline in nearly a year in May as petroleum costs plummeted, according to a government report on Tuesday that bolstered views of tame inflation and low interest rates.

Import prices fell 0.6 percent, the biggest decline since July, after rising by a revised 1.1 percent in April, the Labor Department said.

Although the decline was less than economists' expectations for a 1.2 percent fall, it was the first drop since February. April import prices were previously reported to have increased 0.9 percent. In the 12 months to May, import prices rose 8.6 percent.

The monthly decline in import prices reflected a 5.0 percent fall in the cost of imported petroleum and petroleum products, the largest drop since December 2008, after a 3.7 percent gain in April.

Excluding petroleum, import prices rose 0.5 percent after rising by the same margin in April.

Strength in the U.S. dollar is also helping to keep inflation pressures muted and this should allow the Federal Reserve to renew its low interest rate pledge at next week's policy meeting to nurse the economy's recovery.

The Labor Department report showed export prices unexpectedly increased 0.7 percent last month after rising 1.2 percent in April. Analysts had expected export prices to be flat in May. In the 12 months to March, export prices rose 5.8 percent.

(Reporting by Lucia Mutikani, Editing by Chizu Nomiyama)