Prime Minister Lee Hsien Loong has called on ASEAN countries to press on with the work of creating a more integrated region, even as he said the group had made good progress on this front.
He made the remarks at a closed-door plenary session of the 26th ASEAN Summit in Kuala Lumpur.
They came after ASEAN Secretary-General Le Luong Minh said member-nations have implemented more than 90 per cent of what needed to be done for an ASEAN Community, which would be declared by the end of this year.
"The remaining action lines are the most difficult to do, and we must focus on them because the most difficult items are the ones which will yield significant benefits," Mr Lee said.
"We should give them a strong push over the finish line."
He highlighted three issues he felt were important for the region to advance.
First, greater liberalising of the service sector. Members are negotiating a final agreement on it, but many still find it hard to get the sector to open up to the degree that had been agreed on.
Second, air transport services. The region has made good progress in implementing the ASEAN open skies agreements, but members have to complete its ratification by the end of this year.
Third, the Regional Comprehensive Economic Partnership (RCEP) - a free trade agreement ASEAN members as well as China, India, Japan, South Korea, Australia and New Zealand are negotiating.
Mr Lee said talks on the RCEP have been slow so far, adding: "ASEAN has to show leadership and aim for a high-quality agreement rather than set ourselves a low bar, because this is a major trade-liberalisation initiative which will benefit all our peoples in South-east Asia."
ASEAN leaders had extensive discussions during the session on the establishment of the ASEAN Community and its future direction, ASEAN chairman and Malaysian Prime Minister Najib Razak told reporters later.
Mr Lee noted that while growth remained a key focus for the region, it had to be sustainable. Otherwise, people's lives and health would be affected.
On the haze, he welcomed Indonesian President Joko Widodo's commitment to tackle the issue of forest fires. The next step was to put into operation the haze-monitoring system and develop more joint projects, he added.
Beyond this year, Mr Lee suggested three priorities members could focus on.
First, to deepen economic co-operation, such as by tackling more challenging issues like non-tariff barriers.
Second, widening co-operation to areas such as disaster management, regional nuclear safety and cross-border pollution.
Third, strengthening the organisation and secretariat of ASEAN.
He noted that officials have discussed improving the efficiency of ASEAN processes for more meaningful talks.
He also thanked his counterparts for their tributes to Singapore's first Prime Minister, Mr Lee Kuan Yew, who died on March 23.
"He, together with other pioneering ASEAN leaders, including pioneering PM Tun Abdul Razak, worked hard to make ASEAN a success," Mr Lee said.
"They fostered peace and stability, and set us on a path of regional integration. It is incumbent on us to build on their legacy."