Thailand's Prime Minister Srettha Thavisin on Monday said he was "very worried" about the weaker-than-expected economic growth in the third quarter.

"We will focus on improving the fourth quarter," he told reporters.

The Thai economy grew 1.5% in the July-September quarter from a year earlier, the National Economic and Social Development Council (NESDC) said, well under the 2.4% growth predicted by economists in a Reuters poll. (Reporting by Chayut Setboonsarng and Panarat Thepgumpanat)