SINGAPORE -- An undercurrent of unease over the intensifying superpower rivalry and the new AUKUS alliance is running through the Association of Southeast Asian Nations' summits this week, with some members taking the opportunity to voice their concerns.

In a highlight of three days of virtual meetings, ASEAN will host the East Asia Summit on Wednesday evening with leaders from two of the three AUKUS members -- the U.S. and Australia -- along with China, India, Japan, New Zealand, Russia and South Korea. This will be the first such summit since Washington and Canberra forged the new trilateral grouping last month with the U.K., shaking the region's security landscape and drawing the ire of multiple governments, not least the one in Beijing.

Malaysia and Indonesia have been particularly outspoken on their misgivings about the deal, which will give Australia nuclear submarine technology. They have argued it could stoke a regional arms race. In some ASEAN capitals, there is also a fear that the alliance and U.S.-China competition more broadly will undermine the bloc's relevance and "centrality."

Comments from Malaysia during ASEAN's own summit on Tuesday, however, indicated that leaders were unable to agree on a unified stance.

"Malaysia finds it regrettable that there was a lack of unity on issues that could impact regional peace, stability and security, namely AUKUS and [the Southeast Asia Nuclear Weapon-Free Zone] treaty," Prime Minister Ismail Sabri Yaakob said. He added that it was "regrettable that ASEAN was unable to come up with a statement on the establishment of the trilateral security arrangement."

The chairman's statement from the summit, issued late Tuesday, did not include the term "AUKUS," only noting "the importance of strengthening ASEAN centrality [and] unity in our engagement with ASEAN's external partners."

Still, several leaders have expressed, or at least alluded to, a wariness of AUKUS this week.

In an ASEAN-Australia Summit on Wednesday, Indonesian President Joko Widodo told Australian leader Scott Morrison that Jakarta is worried about AUKUS and the development of Australian nuclear submarines, which could trigger increased rivalry in the region, according to Widodo's press office.

"We must be able to build a culture of conflict into a culture of peace, a trust deficit into a strategic trust," Widodo said.

Australian Prime Minister Scott Morrison, center, attends a virtual meeting with ASEAN members on Oct. 27, in which he sought to reassure his counterparts about AUKUS. (Photo courtesy of Brunei government)

Earlier, at the ASEAN Summit on Tuesday, Thai Prime Minister Prayuth Chan-ocha said the group "must collectively raise clear and coordinated voices" on ASEAN centrality -- a core concept that positions the bloc as the heart of the region's security architecture. He stressed the need to strengthen ASEAN-led mechanisms by employing the ASEAN Outlook on the Indo-Pacific -- the grouping's regional vision -- as a tool to encourage the major powers to engage constructively.

In a similar vein, Singaporean Prime Minister Lee Hsien Loong said that "the various regional architecture formulations by external partners" should support ASEAN centrality and unity, and complement the existing ASEAN-centric regional architecture. "We hope that any new security arrangements will contribute constructively to regional peace and stability."

Likewise, Philippine President Rodrigo Duterte -- whose government has been arguably the most supportive of AUKUS in Southeast Asia -- said pacts like AUKUS "must complement and not complicate our working methods for cooperation."

For their parts, Australia and the U.S. have made a point of reassuring ASEAN counterparts.

In the ASEAN-Australia meeting, Morrison insisted AUKUS "does not change Australia's commitment to ASEAN or the ASEAN Outlook on the Indo-Pacific," according to a transcript released by his office. "Indeed, it reinforces it. It reinforces the backing that we have for an ASEAN-led regional architecture. These commitments are stronger than ever."

Morrison also vowed that "AUKUS does not change Australia's deep, long-standing commitment to nuclear nonproliferation -- Australia does not want and will not seek nuclear weapons, as I've assured all ASEAN members."

Meanwhile, U.S. President Joe Biden told ASEAN leaders on Tuesday that the bloc is "essential to the regional architecture of the Indo-Pacific," that Washington is "committed to ASEAN's centrality" and that it "strongly supports" ASEAN's Indo-Pacific vision.

Biden's participation in the ASEAN-U.S. Summit was the first by a president since 2017, after which his predecessor Donald Trump skipped the meetings. Wednesday's East Asia Summit would mark the first U.S. presidential attendance since 2016.

Biden suggested in Tuesday's summit that he would visit the region in person soon. "You can expect to see me personally showing up and reaching out to you," he said.

ASEAN leaders did acknowledge the benefits of Western engagement in the region, from advancing efforts to recover from the pandemic to building greener, more digital societies.

"Malaysia noted with appreciation Australia's strong support for ASEAN's efforts to mitigate the impact of COVID-19," Ismail Sabri tweeted after the meeting with Morrison.

Singapore's Lee laid out ways to strengthen ASEAN-Australia ties, once again emphasizing centrality. "ASEAN and Australia share similar strategic regional outlooks," he said. "Singapore welcomes new regional architecture formulations that support ASEAN centrality, deepen economic integration, and promote a stable and secure Asia-Pacific region and a rules-based order, including the 1982 U.N. Convention on the Law of the Sea."

Holding Morrison to his word, Lee said, "We welcome Australia's assurance that its AUKUS partnership with the U.S. and U.K. will be consistent with these criteria."