The White House has renewed its call for North Korea to halt provocative rhetoric, but says the United States has not detected any military mobilizations by Pyongyang to back up threats against the U.S. and South Korea.
Tensions remain high amid North Korean threats against South Korea, and South Korean President Park Geun-hye's vow to make a strong military response to any attack by Pyongyang.
In recent days, the United States sent B-2 and F-22 stealth aircraft to South Korea as part of joint military exercises with its Asian ally.
On Monday, White House press secretary Jay Carney said those flights were part of "prudent" and important steps to reassure allies and demonstrate resolve to Pyongyang.
But he said the U.S. and its allies look closely at both North Korean rhetoric and the situation on the ground, and so far Washington has not seen any large-scale changes.
"Despite the harsh rhetoric we are hearing from Pyongyang, we are not seeing changes to the North Korean military posture, such as large-scale mobilizations and positioning of forces. Now we take this seriously, I have said that in the past, and we are vigilant and we are monitoring the Korean situation very diligently," he said.
Carney sidestepped a question as to whether the U.S. has been in touch with Pyongyang through the United Nations.
There also were no specifics on any direct White House communications with China. Carney said only that North Korea is frequently a topic in discussions between U.S. and Chinese officials.
President Obama's spokesman called participation of advanced U.S. military aircraft in joint exercises part of steps to reduce pressure on Seoul to take unilateral action. He said the U.S. believes Pyongyang has clearly received the message being sent by Washington and U.S. allies.
"I think it is pretty clear that they know what the position is that we hold and that our allies hold in terms of both provocative actions and bellicose rhetoric on one hand, and then what steps they could take and what they need to do to reduce their isolation and improve the lot of their people," he said.
North Korea has said it is in a "state of war" with the South. Pyongyang declared the 1953 Korean War armistice invalid, and threatened to launch preemptive nuclear strikes on the U.S. mainland and American bases in the Pacific.
Carney said the U.S. is committed to maintaining peace and security in the region, and said Pyongyang should stop its provocative threats, adding its pursuit of nuclear and missile programs does not make North Korea more secure.
The United States, meanwhile, is further strengthening its naval capabilities in international waters off North Korea.
A Defense Department official told VOA that the a guided missile destroyer is in position off the southwest coast of the Korean Peninsula.
The official called this "a prudent move that provides greater missile defense options should they become necessary."