Russian archaeologists say they have found the long-lost capital of the Khazar kingdom in southern Russia, a breakthrough for research on the ancient Jewish state.

"This is a hugely important discovery," expedition organiser Dmitry Vasilyev said from Astrakhan State University after returning from excavations near the village of Samosdelka, just north of the Caspian Sea.

"We can now shed light on one of the most intriguing mysteries of that period - how the Khazars actually lived. We know very little about the Khazars - about their traditions, their funerary rites, their culture," he said.

The city was the capital of the Khazars, a semi-nomadic Turkic peoples who adopted Judaism as a state religion, from between the 8th and the 10th centuries, when it was captured and sacked by the rulers of ancient Russia.

At its height, the Khazar state and its tributaries controlled much of what is now southern Russia, western Kazakhstan, eastern Ukraine, Azerbaijan and large parts of Russia's North Caucasus region.

The capital is referred to as Itil in Arab chronicles but Mr Vasilyev said the word may actually have been used to refer to the Volga River on which the city was founded or to the surrounding river delta region.

Itil was said to be a multi-ethnic place with houses of worship and judges for Christians, Jews, Muslims and pagans. Its remains have until now never been identified and were said to have been washed away by the Caspian Sea.

Archaeologists have been excavating in the area if Samosdelka for the past nine years but have only now collected enough material evidence to back their thesis, including the remains of an ancient brick fortress, he added.

"Within the fortress, we have found huts similar to yurts, which are characteristics of Khazar cities.... The fortress had a triangular shape and was made with bricks. It's another argument that this was no ordinary city."

Around 10 university archaeologists and some 50 students took part in excavations in the region this summer, which are partly financed by the Jewish University in Moscow and the Russian Jewish Congress.

- AFP