South Korea's president has begun an official visit to China.

Lee Myung-bak arrived in Beijing Monday. He is expected to hold extensive talks with Chinese President Hu Jintao. Mr. Lee is also expected to meet with China's top legislator during his three-day trip.

Beijing and Seoul are closely watching nuclear-armed North Korea amid concerns of instability after the death of North Korea's longtime leader Kim Jong-Il.

China has thrown its support behind Mr. Kim's son and successor, Kim Jong-Un.

Mr. Lee has expressed a wish for better relations with the North, but has also promised a strong reaction to any provocation.

The North has harshly criticized the South's leaders since Kim Jong-Un was declared successor to his father, threatening unspecified retaliation against Seoul for perceived insults during official mourning for Kim Jong-Il.

Tensions between the two Koreas rose more than a year ago when Seoul accused Pyongyang of sinking a warship near the disputed sea border, known as the Northern Limit Line. Forty-six South Korean sailors were killed in the March 2010 attack.

Relations worsened after the North bombarded South Korea's Yeopyeong island in November 2010, killing four people.

North Korean officials have sent a message to the world not to expect any changes in the communist country's policies.