The lucrative tourism sector, which accounts for about 10% of the economy, suffered its biggest drop in visitors in June - the first full month after the army took power on May 22 in a bid to end tensions and get economic activity going again.
International arrivals in July totalled 1.91 million, compared with 1.56 million in June and 2.15 million in July 2013, according to data posted on the department's website late Friday.
Arrivals from China, the country's single biggest visitor source accounting for 18% of all tourists in July, tumbled 25.3%.
For the first seven months of the year, international arrivals totalled 13.62 million, down 10.7% from 15.26 million a year earlier, an even steeper drop than the first-half decline of 9.9%.
By region, arrivals from East Asia were down 17.6% for the first seven months of 2014 from a year earlier. Arrivals were up 3.1% from Europe and 9.6% from Africa. Declines were seen from the Americas (3.5%), the Middle East (6.9%), South Asia (10%) and Oceania (1.6%).
Arrivals from Asean, which account for 26.8% of all foreign tourists, were down 9.8%.
Among large individual markets, Malaysia accounted for 9.8% of all visitors to Thailand and arrivals through July were down 19.9% from a year earlier to 1.34 million. Visitors from Japan (5% of the total) were down 21%, South Korea (4.6% share) declined 17%, the United States (3.3% share) fell 5.2% and Australian arrivals (3.6% share) were off 1.1%.
The United Kingdom, with a 4% share of all visitors to Thailand, was one of the few large markets to record a gain, of 6.2%.