American duo 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.
There has been hostility in the region for weeks because of United Nations sanctions imposed on North Korea for a nuclear test.
And 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 No 7 Louis Oosthuizen of South Africa will be the highest-ranked player at the event which is due to start on Thursday.
Former US PGA champion Yang Yong-eun of South Korea, 1999 Open winner Paul Lawrie and former European Ryder Cup player Paul Casey are also entered in the tournament.