By Tatyana Shumsky 

Gold and silver futures plunged Tuesday as concerns about Greece's potential exit from the euro buoyed the dollar and swept precious metals prices lower.

Gold for August delivery, the most actively traded contract, fell $20.60, or 1.85, to $1,152.60 a troy ounce on the Comex division of the New York Mercantile Exchange. The contract fell to $1,151.50 an ounce, the lowest level since March 18.

Silver for September delivery fell to $14.825 an ounce, the lowest level since Dec. 1, and was recently trading down 5.6% at $14.865 a troy ounce.

Precious metals have been under pressure in recent weeks, as expectations for higher interest rates in the U.S. damped interest in the zero-yielding assets. The Federal Reserve is expected to raise benchmark borrowing rates in the second half of 2015, the first such move since late 2006. This is bad news for precious metals, which don't pay interest or dividends and will struggle to lure investors from interest-bearing assets like Treasury bonds when rates climb.

In recent days, concerns about Greece's debt and the future of the euro prompted investors to sell the common European currency in favor of the U.S. dollar, adding to the pressure on precious metals prices. Gold and silver are traded in dollars and become more expensive for investors who use other currencies to fund their purchases when the dollar rallies. The WSJ Dollar Index was recently up 0.7% at 87.88.

"Gold is a dollar story. The dollar strength is the biggest pressure on commodities today," said Dave Meger, director of metals trading with High Ridge Futures in Chicago.

The rally in the dollar has also overwhelmed the appeal of gold and silver as safe places to stash cash during periods of economic and financial uncertainty, analysts and investors say.

Some investors are also staying away from precious metals amid optimism the last-ditch efforts between Athens and European creditors will yield a compromise on Greek debt.

"The (precious) metals' pricing continues to suggest that traders are expecting a resolution to Greece's 'bankruptcy'," said Peter Hug, global trading director at Kitco Metals Inc., in a note to clients.

Write to Tatyana Shumsky at tatyana.shumsky@wsj.com