American Ryder Cup golfers Dustin Johnson and Zach Johnson have pulled out of the Ballantine's Championship in South Korea this week because of the political tension in the region.
"They have reached this decision following perceived unrest on the Korean peninsula," the sponsors of the European Tour event said in a statement on Monday.
There has been hostility in the region for weeks because of United Nations sanctions imposed on North Korea for a nuclear test.
On Sunday, a South Korean news agency reported that the North had moved short-range missile launchers to its east coast, apparently indicating it was pushing ahead with preparations for a test launch.
World number seven Louis Oosthuizen of South Africa will be the highest-ranked player at the Ballantine's event in Seoul starting on Thursday.
Former U.S. PGA champion Yang Yong-eun of South Korea, 1999 British Open winner Paul Lawrie and former European Ryder Cup player Paul Casey will also be chasing victory in the tournament which carries a prize fund of 2.2 million euros ($2.88 million).