Mr Turnbull said Ms Suu Kyi had addressed the situation at length during ASEAN talks.
Prime Minister Turnbull said the ability to use encrypted messaging platforms to transmit terrorism instruction material across borders undetected posed a particularly steep challenge for law enforcement, as did with the use of crypto-currencies and shady online crowd sourcing platforms to disguise terrorist financing.
ASEAN leaders also said they were working to provide humanitarian assistance for the continuing crisis involving Muslim Rohingya refugees fleeing Myanmar, with Australia's Prime Minister Malcolm Turnbull saying the country's leader Aang San Suu Kyi addressed the matter "comprehensively" in meetings Sunday.
Australian Prime Minister Malcolm Turnbull also spoke at the conference.
The leaders of Australia and Singapore closed a regional summit on Sunday with a stand against against protectionism, arguing in favour of multi-nation trade deals as fears mount that U.S. plans for new tariffs could stoke a global trade war.
"It's a very complex problem".
With China flexing its muscle, they also committed to enhancing "the scope and sophistication of defence cooperation", while expressing "grave concern" about escalating tensions on the Korean peninsula.
Singapore's Lee said there was hope it could be finalised this year.
"This is a historic opportunity to establish the world's largest trade bloc", he told the leaders meeting on Sunday morning.
ASEAN groups Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam, with Australia, a dialogue partner since 1974.
Turnbull, who delivered his keynote address before Najib, was also on the same page with the prime minister on the importance of having laws that could rein in terror elements, before they get out of control, saying that Asean must work together to develop and implement counter-terrorism legislation consistent with global standards and best practices.
The MoU includes an agreement to try coordinate regional laws around gathering and using electronic evidence to pursue terrorists through a series of ASEAN-Australian workshops.
On board the flght President Jokowi was accompanied by First Lady Iriana, coordinating minister for security, political and legal affairs Wiranto, minister/state secretary Pratikno, foreign minister Retno Marsudi and head of Capital Investment Coordinating Board Thomas Lembong. As an initiative to this project, a knowledge bank of sustainable urban planning ideas will be shared between ASEAN and Australia, he added.
- A scholarship for an Australian undergraduate student to study in an ASEAN country as part of the New Colombo Plan.