Still, the Foreign Ministry's statement was significant in that it was the agency's first on the U.S. since Obama's inauguration, an analyst said.
"The Foreign Ministry is Washington's direct negotiating partner and has not engaged in criticizing the U.S. so far," said Kim Yong-hyun, a professor at Seoul's Dongguk University. "This means they have started expressing pent-up complaints."
However, the ministry's less strident tone than other agencies reflects Pyongyang's willingness for negotiation, Kim said.
"The new administration of the U.S. is now working hard to infringe upon the sovereignty" of North Korea "by force of arms," the statement said. It accused Obama's government of "letting loose a whole string of words and deeds little short of getting on the nerves of the (North) and seriously interfering in its internal affairs."
The statement did not elaborate on the alleged meddling, but Pyongyang has rejected demands from the U.S. and neighboring governments that it drop a missile launch plan, claiming it has the right to send off a satellite as part of its space program.
The North may also have been referring to comments by U.S. Secretary of State Hillary Rodham Clinton last month over a potential power struggle to replace North Korean leader Kim Jong Il, who is believed to have suffered a stroke last year.
The North's statement also called the annual military drills in South Korea "war exercises designed to mount a pre-emptive attack" on the North. It said the country "will take every necessary measure to protect its sovereignty." It did not specify what the measures would be.
North Korea has long claimed that annual exercises are rehearsals for an invasion. Seoul and Washington say the drills are purely defensive.
The 12-day maneuvers, involving 26,000 U.S. troops and an unspecified number of South Korean soldiers, include live-fire drills. The aircraft carrier USS John C. Stennis arrived Wednesday at a naval base in the southern port city of Busan for the exercises.
Tensions on the divided peninsula have also been running high amid fears that Pyongyang might be trying to test-fire a long-range missile capable of reaching U.S. territory.
The North claims what it is trying to launch is a satellite as part of its peaceful space program, and vowed to retaliate against any one seeking to shoot it down.