"The State Security Court sentenced four Syrian Kurds to six-year terms on Sunday for membership of the banned Kurdish Democratic Union Party (PYD) and for plotting to join a part of Syrian territory with a foreign country," the Syrian Observatory for Human Rights said in a statement.

The London-based watchdog named the four as Nasser Ahmed Mohammed, Fawaz Ali, Saud Chikhmus and Abdelrahman Mustafa Mohammed. They were all arrested either last year or early this year.

It called on the authorities to end the 46-year-old state of emergency under which the state security court operates. Its decisions cannot be appealed.

The Syrian authorities routinely accuse clandestine Kurdish parties of separatism even when they campaign for Kurdish cultural and linguistic rights within Syrian borders.

More than 1.5 million Kurds live in Syria, comprising nine percent of the population. They have long sought official recognition of the Kurdish language and culture.