China confirmed to foreign diplomats in Beijing on Monday that North Korean leader Kim Jong-il had visited the country, Japan's Kyodo news agency said, as Chinese state media praised ties with the isolated country.

A source told Reuters at the weekend that Kim and his youngest son -- his presumed heir -- were on a trip to China but there has been no official confirmation from either government.

Kyodo, citing diplomatic sources, said the Chinese Foreign Ministry explained to some Beijing-based diplomats the visit of North Korean leader Kim Jong-il to the country.

The report said that Kim had met Chinese President Hu Jintao, adding that Kim was expected to go back to North Korea later in the day.

In the past, China and North Korea have only publicly confirmed Kim's visits after he has returned home.

A Chinese-language newspaper nonetheless lauded relations between the two countries on Monday.

Maintaining and stabilising the current relationship between China and North Korea is of maximum benefit to China, the popular tabloid the Global Times said in an editorial.

China is the only major supporter for North Korea, which is largely isolated from the international community over its nuclear weapons programme and which has come under further condemnation after South Korea accused it of sinking one of its warships earlier this year.

China's official Xinhua news agency also praised ties between the two, especially the bonds forged between their people during the 1950-53 Korean War.

Those who sacrificed their lives for the China-DPRK (North Korea) friendship should be remembered generation after generation, particularly at a time of changing and complicated regional situations, it said in an English-language commentary.

Kim, 68 and who rarely travels abroad, is reportedly in China for the second time this year. This time he is thought to have brought along his youngest son Kim Jong-un, widely seen as the next head of the family dynasty that has led North Korea since its founding more than 60 years ago.

NO DEFINITE SIGHTINGS

On Monday, police lined the streets in Tumen, a city on China's border with North Korea, in a sign that Kim may visit there or pass through on his way home.

The clues of Kim's travels have been pursued by legions of reporters, especially from the North's neighbours, South Korea and Japan, who study the comings and goings of trains and motorcades, some of them possibly meant to bamboozle the press.

But there have been no definite sightings of Kim.

Kim may be lining up China behind succession plans involving his son, foreign analysts have said. The Workers' Party (WPK), which rubber-stamps big decisions in the North, is due to hold a rare meeting in September that could set in motion succession steps.

The Chinese newspaper blamed outside forces for pressuring North Korea as a way to create trouble for China, the sole major economic and diplomatic supporter of its much weaker neighbour.

The sinking of the South Korean navy ship, in which 46 sailors died, deepened tensions between Pyongyang and Seoul and strained Chinese ties with South Korea.

(Additional reporting by Maxim Duncan in Tumen, China; Editing by Alex Richardson)

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