Prime Minster Shinzo Abe has decided to visit Laos and Cambodia as soon as mid-October, a government source said Sunday.
Abe is set to visit Brunei in early October to attend a summit of the Association of Southeast Asian Nations, the source added.
The three Southeast Asian countries are the only ones in ASEAN that Abe hasn't yet visited since taking office in December.
ASEAN groups Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam.
Abe went to Vietnam, Thailand and Indonesia in January, Myanmar in May, and Malaysia, Singapore and the Philippines in July. His January trip was his first abroad as prime minister.
Abe plans to convene a Japan-ASEAN special meeting in Tokyo in December, the first time the gathering has been held in the capital in 10 years.
The meeting will demonstrate his stance of deepening Japan's relationships with ASEAN, the source said.
The meeting is also aimed at keeping China in check. Beijinghas become increasingly assertive in the East China and South China seas.