SINGAPORE - The Five Power Defence Arrangements (FPDA), which turns 50 this year, needs to remain nimble amid a challenging environment, said Prime Minister Lee Hsien Loong on Thursday (Oct 21).

Noting that the geo-strategic environment will remain in flux, he said: "There will be new threats and geopolitical shifts that upend our operating assumptions and expectations."

He was speaking to defence ministers from the FPDA during a virtual joint call, before the 11th edition of the pact's Defence Ministers' Meeting, its most important decision-making platform.

Set up in 1971 upon British withdrawal, the FPDA created a platform for Singapore, Malaysia, Britain, Australia and New Zealand to consult each other if either Singapore or Malaysia were attacked.

It has since expanded to include nearly annual joint military exercises, cooperation on unconventional threats such as terrorism, humanitarian assistance and disaster relief.

To these, the five nations added a focus on introducing cyber security into FPDA exercises on Thursday.

Defence Minister Ng Eng Hen said the FPDA remains a defence deterrent not targeted at any country, in addition to being a stabilising force for the region.

"The stronger you are, the more friends you have," he said.

The grouping has faced questions over its relevance in recent years, with Singapore and Malaysia now both touting professional armies, a far cry from the state of their armed forces in their early years.

Malaysian Senior Defence Minister Hishammuddin Hussein acknowledged the biggest challenge in the next 50 years "is how to keep us intact".

It could expand to have more influence outside the FPDA by engaging other multilateral blocs, including Asean - a possibility that has been discussed by the five defence ministers, he said.

He added, however, that this "does not mean that we will stray from the basic principles and values that we have stood for."

At the meeting in Kuala Lumpur, the prime ministers of the pact's members reaffirmed their countries' commitment to the FPDA in its jubilee year, speaking virtually in recorded clips.

PM Lee said the FPDA, after offering the two young nations "a valuable security umbrella" and the assurance to develop into stable and prosperous countries in the pact's early years, is now "an established and accepted way for our longstanding and deeply appreciated partners to continue contributing to the peace, stability and regional order in South-east Asia".

British PM Boris Johnson said "Britain will be proud to make an even bigger and more consistent contribution", while New Zealand PM Jacinda Ardern said the FPDA remains a cornerstone of the country's engagement in the region.

Australia PM Scott Morrison said through the FPDA, the country is also committing to an alliance of shared values - a belief in sovereignty, in human dignity, and in a world order that favours freedom.

Malaysian PM Ismail Sabri Yaakob said he hopes the FPDA will continue to address emerging security challenges constructively.

PM Lee said the FPDA takes active steps to reassure neighbours that it is peaceful and inclusive, including inviting non-FPDA regional neighbours, such as Indonesia, to observe military exercises.

Singapore will host the next Defence Ministers' Meeting in 2024.