UN Secretary-General Ban Ki- moon on Thursday expressed his serious concern about the military takeover in Thailand and appealed for "a prompt return to civilian order" in the Asian country.

"The secretary-general is seriously concerned by the military takeover in Thailand," said a statement issued here by Ban's spokesman, the second one pertaining to the country in the past 72 hours.

According to reports, the Thai military on Thursday sized control of the country following months of unrest and widespread protests in the capital Bangkok and other parts of the nation.

Popular demonstrations began in late 2013, with calls for the ouster of Prime Minister Yingluck Shinawatra's administration and implementation of anti-corruption reforms. The military declared martial law two days ago. On May 7, Yingluck reportedly was removed from government after a ruling by the Thai Constitutional Court.

The secretary-general "appeals for a prompt return to constitutional, civilian, democratic rule and an all-inclusive dialogue that will pave the way for long-term peace and prosperity in Thailand," said the statement.

"The secretary-general urges all parties to work together constructively, refrain from violence and respect human rights," it added.