SINGAPORE - Singapore has lodged a strong protest with the Malaysian government over recent actions that impinge on Singapore's sovereignty, and warned that it will not hesitate to take firm action against intrusions and unauthorised activities in the Republic's territorial waters.

The Ministry of Transport on Tuesday (Dec 4) said it noted with grave concern Malaysia's purported extension of the Johor Bahru port limits in a manner which encroaches into Singapore territorial waters off Tuas, through a notice in the Federal Government Gazette.

Over the past two weeks, vessels from the Malaysian Maritime Enforcement Agency and Marine Department Malaysia have also repeatedly intruded into Singapore territorial waters off Tuas, the ministry added.

"Singapore has protested the unauthorised movements of, and purported assertions of sovereignty by these vessels, which are inconsistent with international law," it said in a statement.

"The Republic of Singapore Navy and the Police Coast Guard are safeguarding the sovereignty of Singapore territorial waters and enforcing the security of these waters on a 24/7 basis," it added.

Transport Minister Khaw Boon Wan told reporters the Malaysian actions "are clearly a violation of our sovereignty and international law".

Earlier in the day, Malaysian Transport Minister Anthony Loke had told the Malaysian Parliament that KL had informed Singapore of its intention to take back airspace over south Johor which had been delegated to Singapore to manage, in stages, from next year.

"It is not our stance to take a confrontational approach," Mr Loke said. "But this involves our sovereignty, which the Malaysian government will defend in the strongest terms."

Singapore's Transport Ministry replied that "Singapore respects Malaysia's sovereignty", but noted that international law is clear that cross-border airspace management is not incompatible with sovereignty.

Apart from its Gazette notification on Oct 25 declaring new Johor Bahru port limits, Malaysia had also issued a port circular dated Nov 11 and a notice to mariners dated Nov 22 on these changes.

In response to the notices from Kuala Lumpur, Singapore lodged a strong protest with the Malaysian government.

Singapore has also requested that Malaysia amend its notices "to reflect the sovereignty of Singapore over the waters in question, and that Malaysia refrain from taking any further unilateral action".

The Maritime and Port Authority of Singapore (MPA) also issued a circular on Nov 30 instructing ship masters and owners of vessels to disregard Malaysia's three notices, "which impinge on Singapore's sovereignty".

The Ministry of Transport added: "Malaysia's purported extension of the Johor Bahru port limits and the repeated intrusions by Malaysian Government vessels into Singapore territorial waters are a serious violation of Singapore's sovereignty and international law. These actions are unconducive to good bilateral relations, cause confusion for the international shipping community, and lead to increased navigational and safety risks for all parties."

"Singapore stands ready to engage with Malaysia to resolve these matters amicably, in accordance with international law."

Asked whether there is a concern that the issues over airspace and port limits could escalate, Mr Khaw told reporters that he hoped they would not.

"It is certainly not conducive for bilateral relations. We have so many things that we want to work together on," he said.

As for actions taken by Singapore, he added: "If you intrude into our space, there will be warnings, move on, move away... There are standard rules of engagement."

"We do not want a misunderstanding which leads to unnecessary accident or worse, then suddenly we have a crisis to handle," he said.

"We hope that good sense will prevail."