KUWAIT, Oct 16 (Reuters) - Kuwait's emir ordered the dissolution of parliament on Sunday, saying regional developments and "security challenges" meant the national assembly should choose fresh representatives.

The order was contained in a decree by Sheikh Sabah al-Ahmad al-Sabah published by the Gulf Arab state's official KUNA state news agency.

The agency had no further details. Elections now need to be held under constitutional rules.

KUNA reported the decree as saying the move was linked to regional developments and "security challenges and their different impacts and risks, that require returning to the people - the origin of authority - to choose its representatives to express its directions, ambitions and contribute to facing these challenges."

Kuwait, a regional U.S. ally, has a relatively open political system by Gulf standards and has avoided an uprising like those that have ousted leaders in several Arab states since 2011.

Political stability in Kuwait, a leading OPEC oil producer and exporter, has traditionally depended on cooperation between the government and parliament, the oldest and most powerful legislature in the Gulf Arab states.

Liberals and candidates from some of Kuwait's more marginalized tribes won seats in the last election in 2013, after opposition Islamists and populists boycotted the election.