MOSCOW, March 11 (RIA Novosti) - South Korea and the United States began annual large-scale military exercises on Monday, shortly after a fresh round of UN sanctions was imposed on North Korea last week, Yonhap reported.

The exercise, codenamed Key Resolve, will run through March 21 and involves 10,000 South Korean and 3,500 US troops.

The exercise kicked off after Pyongyang threatened the United States last week with a preemptive nuclear strike, and said it plans to terminate the Korean War Armistice Agreement and warned of retaliatory countermeasures if the United States and South Korea went ahead with the drills.

North Korea cut off a communication hotline with South Korea on Monday, Yonhap said on Monday.

South Korea's unification ministry said the North is not answering calls made through the emergency link set up to ensure prompt, two-way communication to deal with any sudden developments along the land and sea demarcation line that separates the two Koreas.

The fourth set of UN sanctions, adopted on Thursday, is aimed at curbing the activities of North Korean institutions and individuals suspected of funneling money to the communist regime's nuclear and missile programs.

Pyongyang carried out its third nuclear weapon test last on February 12 this year, prompting widespread condemnation from the international community.