The benchmark Kospi index declined 0.3 percent as of 9:05 a.m.in Seoul, while the won weakened 0.3 percent against the dollar.
Brent crude touched its highest since July 2015 after major producers said the global market was on track to rebalance and Turkey said it could cut off a pipeline that carries oil from northern Iraq to the global market, putting more pressure on the Kurdish autonomous region over its independence referendum. Apple, Amazon, Microsoft and Google-parent Alphabet each lost one percent or more.
North Korea's top diplomat said on Monday that a weekend tweet by U.S. President Donald Trump counted as a declaration of war and North Korea has the right to take countermeasures, including shooting down U.S. bombers, even in worldwide space.
The pan-European FTSEurofirst 300 index rose 0.23 percent and MSCI's gauge of stocks across the globe shed 0.39 percent.
The Nasdaq Composite Index fell 0.9% to 6370.59 and the Standard & Poor's 500 Index slid 0.2% to 2496.66.
New York Federal Reserve President William Dudley said Monday that factors restraining price pressures should disappear with time, allowing the USA central bank to maintain its gradual pace of monetary policy tightening, according to Bloomberg.
General Electric gained 1.0 percent following news it sold its industrial solutions business to Swiss-Swedish engineering group ABB for $2.6 billion.
About 6.42 billion shares changed hands in USA exchanges, above the 6.02 billion daily average over the last 20 sessions.
Meanwhile, US government bonds strengthen as both North Korea tensions and the Germany election outcome with Chancellor Angela Merkel's Christian Democrats emerging as the victorious party but with a reduced share rattled investors, prompting demand for traditional safe haven assets.
In the bond market, treasuries moved notably higher, extending the upward move seen last Friday. Gold was up +1.28% to above $1,300 per ounce.