The powerful uncle of North Korean leader Kim Jong Un met both China's president and premier on Friday in a sign that relations between the two countries are back on track after Kim irked Beijing with a rocket launch soon after taking power.

State media have said the six-day visit to China by Jang Song Thaek, the chief of the central administrative department of the Workers' Party of Korea, is a possible prelude to a visit by Kim himself. China remains North Korea's most important ally.

The top-level meetings came after Beijing earlier this week agreed to help Pyongyang revamp two trade zones near the Chinese border.

Since he became North Korea's top leader following his father's death in December, Kim has promoted younger economists to key party positions to help revive his country's economy. North Korea has lagged economically far behind the rest of Northeast Asia, and much of the nation is impoverished outside the capital, Pyongyang.

Beijing also wants to see bolder economic reforms under the young Kim to lessen North Korea's reliance on hand-outs.

A few months ago, relations between the two allies were strained. North Korea drew strenuous objections from China, the United States, Japan and others by testing a rocket in April because they feared it would add to tensions on the Korean Peninsula between the North and the South. Analysts said North Korea did not give Beijing advance notice of the launch, which particularly irked them.

Jang is a vice chairman of the powerful National Defense Commission. He also is seen as a leading economic policy official.

His meetings with President Hu Jintao and Premier Wen Jiabao in Beijing came toward the end of his visit. Hu praised Jang for his "huge amount of work for the friendly relations between China and North Korea as two neighboring countries," the official China News Service reported.

Wen told Jang that the China-North Korea friendship has endured historical tests and is a shared treasure to be "doubly cherished." He said Jang's visit will deepen the relations between the two ruling parties and the two nations, according to CNS.

Jang met Chinese commerce ministry officials earlier this week to discuss the development of two special economic zones in North Korea.

The ministry said the two sides signed a number of cooperation agreements to further develop the zones _ Rason on the Korean Peninsula's northern tip, and Hwanggumphyong, an island in the Yalu River that marks their border to the southwest.

Rason would be developed into a manufacturing base, logistics center and tourism hub, and the Hwanggumphyong zone would focus on information technology, tourism, agriculture and garment manufacturing, it said.

Rason has recently begun to develop thanks to Chinese infrastructure projects, but Hwanggumphyong has languished since ground was broken last year.

On Thursday, Jang met with Wang Jiarui, the head of the international department of the Communist Party of China Central Committee. Wang said China is committed to strengthening and developing the friendly and cooperative relations between the countries, and Jang said Pyongyang wants to see the friendship strengthen, the official Xinhua News Agency said.