Thai Airways International will raise frequencies on four routes, starting from 25 October.
The carrier says it will raise the Bangkok-Colombo frequency to daily, up from five-times weekly. It will also increase its Bangkok-Ho Chi Minh City service from twice-daily to 17-times weekly, and introduce a third-daily Bangkok-Phnom Penh service.
This will then be followed by a third-daily Bangkok-Vientiane service on 1 January 2016.
Its Bangkok-Kuala Lumpur service will also be cut from 18-times weekly to twice-daily from 25 October, it adds.
FlightMaps Analytics shows that Thai competes with Bangkok Airways on routes from Bangkok to Phnom Penh and Vientiane.