Singapore warned Malaysia yesterday it was ready to defend its interests after a flare-up of maritime tensions, the latest sign of fraying ties since a change of government in Kuala Lumpur.

Addressing Parliament yesterday, Singapore's foreign minister Vivian Balakrishnan reported "daily intrusions" by Malaysian government vessels, which have been in the waters off western Singapore since November. He also took issue with a high-profile visit by a Malaysian chief minister, who boarded one of the vessels on Jan. 9. Balakrishnan said Singapore has protested the visit and called off a joint ministerial meeting in response.

"Our neighbors must not believe that they can take actions without impact, without consequences on themselves," he said. "And any country dealing with Singapore must not assume that it is cost-free to embark on any adventures or antics against us. There will be consequences." Asked to elaborate on the consequences, Balakrishnan said he would not "enumerate them now."

The two countries, which were briefly merged in 1963, are locked in disputes over territorial waters and airspace. They have agreed to try to resolve these peacefully. Balakrishnan met his Malaysian counterpart, Saifuddin Abdullah, in Singapore last week. They announced a working group on tensions in the waters, which are less than 24 nautical miles, or about 44 kilometers, wide. A day later, Osman Sapian, the chief minister of a state in Johor near Singapore, visited a vessel anchored in the contested waters.

"It undermined the goodwill and trust that is necessary for further cooperation between the two countries, and especially cooperation involving Johor," Balakrishnan said. Since Malaysian Prime Minister Mahathir Mohamad returned to power last year, the country has postponed a high-speed rail project that would cut travel time between Singapore and its capital, Kuala Lumpur. Balakrishnan said Malaysia is also pressing to raise the price of water that it supplies to Singapore.