BANGKOK (Reuters) - Thailand's economy grew a much less-than-expected 0.6 per cent in July-September quarter from the same period a year ago, and expanded 1.1 per cent from the previous three months, the planning agency said on Monday.

Southeast Asia's second-biggest economy expanded 0.2 per cent in the first nine months, the agency said.

The army seized power on May 22 in a bid to end months of political unrest and kick-start the sputtering economy, but progress has been limited so far.

A Reuters poll of economists had forecast year-on-year growth of 1.0 per cent in the rhid quarter and on-quarter growth of 1.8 per cent.

The National Economic and Social Development Board (NESDB), which compiles GDP data, revised quarter-on-quarter April-June growth to 1.1 per cent from 0.9 per cent stated earlier.