Several Asian markets fell Monday after North Korea said it had conducted a nuclear test, rattling investors' nerves and heightening regional tension. But as trading progressed, markets recovered modestly.

South Korea's benchmark Kospi index plunged as much as 6.3 percent before paring losses to trade 1.4 percent lower at 1,383.54 in early afternoon trading.

North Korea announced that it had successfully carried out an underground nuclear test, weeks after threatening to restart its rogue atomic program. The country's official Korean Central News Agency called it "part of measures to bolster its nuclear deterrent for self-defense."

Seismologists from the U.S., South Korea and Japan reported earthquakes in a northeastern area, where North Korea conducted a nuclear test in 2006.

Hong Kong's Hang Seng index was down 0.3 percent at 17,005.66, and markets in Australia and mainland China also fell.

Japanese stocks held most of their gains in early afternoon trading, with the Nikkei 225 index up 1.1 percent at 9,323.58. Markets in Taiwan, Singapore and the Philippines also were up slightly.

U.S. stock index futures were flat to slightly lower after Wall Street slid Friday as early gains built on better earnings reports from retailers faded away amid anxiety about the outlook for the American economy -- a vital export market for Asia.

Investors were looking ahead to key U.S. economic reports this week, including home sales, big-ticket manufactured goods and consumer confidence. American financial markets will be closed on Monday for the Memorial Day holiday.

On Friday, the Dow Jones industrial average fell 14.81, or 0.2 percent, to 8,277.32. The S&P 500 index slipped 1.33, or 0.2 percent, to 887.00, and the Nasdaq composite index lost 0.2 percent to 1,692.01.

Dow futures were unchanged at 8,260, while S&P 500 futures were down 2.4 points, or 0.3 percent, at 882.50.

Oil prices slipped Monday in Asia. Benchmark crude for July delivery was up 26 cents to $61.41 a barrel in electronic trading on the New York Mercantile Exchange.

In currencies, the dollar edged down to 94.66 yen from 94.76 late Friday. The euro held steady at $1.3993.