Updated

North Korean troops brandished weapons given to them by new leader Kim Jong Un as they carried out live-fire drills near the disputed sea border and Pyongyang expressed more anger over joint U.S.-South Korean military exercises.

The Associated Press was among select media allowed to observe drills this week on North Korea's southwestern coast, which faces disputed waters where the Koreas have fought three bloody sea battles since 1999. A North Korean shelling that Pyongyang said was provoked by South Korean live-fire drills on nearby Yeonpyeong Island killed four South Koreans in November 2010.

North Korea state media and senior officials have issued a string of angry statements about the U.S.-South Korean drills set to run through April, raising worries that friction between the Koreas will complicate efforts to settle a long-running nuclear standoff. Washington has said that better inter-Korean ties are crucial to the success of nuclear diplomacy.

The tension between North and South comes before envoys from the United States and North Korea meet Wednesday in Beijing to discuss technical details about the distribution of 240,000 metric tons of food aid promised by the U.S. In an agreement reached last week, North Korea will receive U.S. food aid in return for it freezing nuclear activities and allowing back U.N. nuclear inspections.

The nuclear deal's announcement raised hopes for improved ties between Washington and Pyongyang and for a resumption of dormant six-nation talks on curbing Pyongyang's nuclear ambitions. The talks involving the Koreas, the U.S., China, Russia and Japan have been deadlocked since North Korea pulled out in April 2009.

As young leader Kim Jong Un seeks to bolster support, he has toured the heavily armed border with South Korea and visited a number of military units.

North Korea calls the U.S.-South Korean maneuvers preparation for an invasion and an affront because they are happening during the semiofficial 100-day mourning period after Kim Jong Il's death. Seoul and Washington say their exercises are routine and defensive in nature.

North Korea has also threatened revenge against South Korean President Lee Myung-bak, who ended a no-strings-attached aid policy when he took office in 2008. North Korea has expressed anger over a South Korean military unit near Seoul recently posting threatening slogans beneath portraits of Kim Jong Un and his father.

During drills Sunday and Monday, North Korean military commanders warned of a harsher attack than the 2010 shelling.

"We only fired a small number of artillery last time. We will mobilize all our corps' artillery pieces to turn them into a real sea of fire this time," Col. Gen. Pyon In Son, commander of the 4th Corps of the Korean People's Army, told the AP.

State media said on Feb. 26 that Kim Jong Un visited 4th Corps units and ordered troops there to launch a powerful retaliatory strike against South Korea if provoked. The units visited by Kim include a battalion that shelled Yeonpyeong Island in 2010, according to the Korean Central News Agency.

Under gray skies, with North Korea's brown coastal mountains looming above them, troops chanted "Let's beat rabid dog Lee Myung-bak to death." Others raised North Korea's blue, red and white national flags and brandished silver weapons that officers said were gifts from Kim Jong Un during his recent visit.

White smoke billowed from tanks and sparks flew from rockets, with artillery guns pointing at South Korea's Baengnyeong Island, which is visible from the North Korean coast and is near Yeonpyeong. Local residents draped camouflage nets over their shoulders as troops fired.

South Korea's Defense Ministry said Tuesday it had no knowledge of the North Korean drills.

The Korean peninsula remains in a technical state of war because the armistice that ended the 1950-53 Korean War has never been converted to a peace treaty.