BANGKOK (Reuters) - Thailand's military government said on Monday it will prosecute cases concerning national security and royal insult in civilian courts instead of military courts, a change a rights group said was window dressing before a U.N. review.

Prosecution for dissent and royal insult have risen since the military seized power in a 2014 coup with the junta choosing to try such cases in military courts.

The military declared when it took over it considered violations of a strict lese-majeste law, which makes it illegal for anyone to "defame, insult or threaten the king, the queen, heir-apparent or regent", a matter of national security.

Those convicted under the law face up to 15 years in prison.

Students and democracy activists have also been prosecuted in military courts for campaigning against military rule under a sedition law.

According to an order signed by junta chief Prayuth Chan-ocha, future cases relating to national security and lese-majeste would be prosecuted in civilian courts because of "an improving situation and cooperation from the public for the past two years".

"Cases that are pending, or currently in progress, will still be under the jurisdiction of the military courts," junta spokesman Winthai Suvaree told Reuters.

The United States and European Union both downgraded diplomatic ties with Thailand following the 2014 coup. Since then they, as well as the United Nations, have on occasion expressed concern about human rights.

Thailand defends its human rights record saying prosecutions are undertaken according to its laws.

Rights groups say the change was aimed at addressing such concerns and would not make a big difference as civilian courts were known to hand out heavy sentences in cases of royal insult.

"This decision is just window dressing ahead of Thailand's Universal Periodic Review (UPR) in front of the U.N. Human Rights Council later this month," said Sunai Phasuk, Thailand researcher at Human Rights Watch.

"This decision is to show the UPR panel that the junta has made attempts to address the human rights concerns expressed earlier this year," he told Reuters.

Thailand defended its human rights record in front of the Human Rights Council in May this year after some member states noted what they saw as a deteriorating rights situation.

(Reporting by Cod Satrusayang and Panarat Thepgumpanat; Editing by Robert Birsel)