THE open declaration by the United States and Japan in their revised defence pact that the Taiwan Strait belonged in their joint security ambit did not take China by surprise, but would surely sour its relations with both.

The designation of Taiwan as a Common Strategic Objective (CSO) by both countries, which potentially puts the island under their defence umbrella, represented the most significant alteration since 1996 to the US-Japan Security Alliance forged in the early 1960s.

The US had long been concerned about Beijing's threat to use force to prevent Taiwan from seceding, but until the new defence pact signed during the ""two-plus-two'' meeting yesterday in Washington, Japan had shown no desire to side openly with the US.

Although the aim of the meeting between US Secretary of State Condoleezza Rice, Defence Secretary Donald Rumsfeld and their Japanese counterparts was to call for Japan to take a greater role with US forces in the world, their main accent seemed to be on the Taiwan Strait.

The agreement could help lay the groundwork for Japan, which is constitutionally forbidden to take part in war, to extend as much cooperation as it legally can, including logistical support such as transportation and medical rescue operations behind the lines of combat.

Signing on behalf of Japan yesterday were Japanese Defence Ag ency chief Yoshinori Ono and Foreign Minister Nobutaka Machimura.

Politicians and analysts in both countries called the move a demonstration of Japan's willingness to confront the rapidly growing might of China.

Said Mr Shinzo Abe, the acting secretary-general of Japan's ruling Liberal Democratic Party: ""It would be wrong for us to send a signal to China that the US and Japan will watch and tolerate China's military invasion of Taiwan.''

Taiwan appeared much delighted by the agreement as it had long been promoting a Washington-Tokyo-Taipei military alliance. It also construes it as a recognition that the island enjoys sovereignty and is not subject to the rule of mainland China.

Taiwanese Vice-President Annette Lu told reporters yesterday:"" This shows that Taiwan's sovereignty is receiving international attention.''

But Beijing did not seem to be taken aback by the development.

A Chinese source told The Sunday Times that the move merely confirmed Beijing's belief that the US and Japan would intervene to thwart its military bid to prevent Taiwan's secession should peaceful means fail.

If there is anything surprising, it is the decision of Washington and Tokyo not to be ambiguous anymore in their strategic intent about Taiwan and opt for ""strategic clarity''.

The source said that China did not have any illusion at all that the US-Japanese pact would leave out Taiwan.

When the pact was first drawn up in the 1960s, an official Japanese source had already pointed out that its covered ambit
extended from Japan to the Philippines. That certainly included Taiwan, which lies midway between both. But the Japanese did not admit that.

By being ambiguous, Japan had been able to avoid irritating China. But it showed its hand yesterday in the declaration.

""Right from its birth, the US-Japan mutual defence pact was forged with an eye on China, though the focus varied with time,'' said the source.

""China had never underestimated the potential hostility of the pact, whether or not it was mentioned in it,'' said the source.

So militarily, China is prepared for the worst scenario. That said, the source admitted that Beijing was still upset by the
signing.

It showed that its sending of senior officials to the US and Japan to explain the anti-secession law aimed at Taiwan had failed to convince them that it was not an aggression-driven document.

Beijing suspected that the pact was timed to pre-empt the law, which would be passed a few weeks from now.

It could also produce an incipient form of Washington-Tokyo- Taipei military alliance longed by Taiwan, and greatly complicate Beijing's effort to solve the Taiwanese issue peacefully.