Sunday's military exercises, which will include five other U.S. vessels as well as U.S. and South Korean ground forces, were announced over the summer after the sinking of a South Korean navy vessel in an attack widely blamed on North Korea. But the starting date was finalized only this week in response to the artillery barrage, officials said.
In a statement, the U.S. military command in South Korea said the exercises were "defensive in nature" and meant to demonstrate "our commitment to regional stability through deterrence."
A Pentagon official said, "The dates were not officially set until early this week after this artillery duel lent a higher sense of urgency to it." He added that other steps might be announced in coming days in response to the artillery attack.
Tuesday's attack followed the disclosure over the weekend that North Korea was building a uranium enrichment plant at its nuclear site in Yongbyon, news that suggests the secretive regime is seeking a second method of building nuclear weapons.
That disclosure, followed by the attack on the island, stirred wide speculation that North Korea was seeking to pressure the U.S. to agree to further diplomatic concessions and aid.
There was also talk that Pyongyang might want to make a show of force to help establish military and popular support for Kim Jong Eun, the son of and presumed successor to North Korean leader Kim Jong Il.
Senior U.S. officials refused to speculate publicly, however. Gates told reporters that he had no answer for any question about North Korea that began with "Why."
Another U.S. official acknowledged that the North Koreans have often launched provocations "to try to get other nations to sit down and talk. That could be what's going on here, but it's hard to tell."
Several officials said Tuesday that they found the events alarming because of the North's apparent willingness to risk military confrontation and its interest in expanding its nuclear program.
At the same time, officials did not indicate any greater willingness to bend to North Korean pressure to return to the negotiating table.
Administration officials have insisted for months that they will not resume talks until there are signs that North Korea is willing to wind down its nuclear program.
Michael Green, a former top Asia advisor to President George W. Bush who is now with the Center for Strategic and International Studies in Washington, said the North Koreans were "really pushing hard to create a crisis."
He said U.S. strategists have long tried to imagine how military encounters could lead to war on the Korean peninsula, and they have regularly considered the possibility that the North might begin shelling the island.
"This was a step that we thought was not too far from total war," he said.
Analysts said the developments put China in an embarrassing position because Beijing has repeatedly resisted international attempts to punish the North.
The Chinese argued this spring that it was a mistake to penalize North Korea after the sinking of the warship.
Green said China's unwillingness to penalize North Korea may have been read by Pyongyang as a green light for further action.
L. Gordon Flake, a longtime Korea analyst at the Maureen and Mike Mansfield Foundation in Washington, said China had been put in "a really rough position" by the developments.
"My guess is there's going to be a real reevaluation going on in China," he said.
Richter and Cloud reported from Washington and Glionna from Seoul. Times staff writer Ken Dilanian in Washington and Sergei Loiko in Moscow contributed to this report.