Chinese PM visits Seoul as Korea crisis continues
Chinese Prime Minister Wen Jiabao is visiting South Korea amid continuing tension over the sinking - allegedly by North Korea - of a South Korean warship in March.
The issue is expected to dominate Mr Wen's talks on Friday with the South Korean President, Lee Myung-bak.
International investigators have blamed North Korea for sinking the warship.
But China has so far refused to join in the widespread condemnation of its old ally, Pyongyang.
The Chinese state news agency Xinhua quoted the Chinese ambassador to South Korea, Zhang Xinsen, as saying the visit would "strongly boost" ties between the two countries.
The BBC's correspondent in Seoul, John Sudworth, says however, that China is in an uncomfortable position.
He says China's refusal, so far, to join the strong, international condemnation of North Korea is causing frustration in Seoul.
There are calls for China to come off the fence and choose between its old, cold war alliance with Pyongyang and its new role as a modern, global power.
Some news reports suggest that Mr Wen will, albeit subtly and carefully, move closer to the South Korean position on this visit, choosing a form of words that at least placates some of the anger.
But, our correspondent adds, China's priority is stability on its borders and it will be reluctant to sign up to anything it thinks will provoke its North Korean neighbour.
Meanwhile, Japan has said it is tightening its already stringent sanctions against North Korea.
It said it was lowering the amount of cash which individuals can send to North Korea without declaring it from 10m yen (£110,000: £75,000) to 3m yen.
The parliament in Tokyo also passed a bill to enable the Japanese coastguard to inspect vessels on the high seas suspected of carrying North Korean weapons or nuclear technology, in line with a 2009 UN Security Council resolution.
The Associated Press news agency quoted the head of the Public Security Intelligence Agency as saying he had ordered officials to keep a closer eye on the some one million North Koreans living in Japan.
Since being accused of the torpedo strike on the South Korean ship, North Korea has said it will scrap an agreement aimed at preventing accidental naval clashes with South Korea.
It also warned of an immediate attack if the South's navy violated the disputed Yellow Sea borderline.
On Tuesday, North Korea announced it would sever all ties with the South.
The Yellow Sea was the site of deadly naval skirmishes in 1999 and 2002.
The two states are technically still at war after the Korean conflict ended without a peace treaty in 1953.