Russia and Georgia have agreed to meet again in January after "useful" but "difficult" talks on Wednesday aimed at reducing tensions between the two countries, international mediators said.

Tbilissi said it had raised the issue of Georgians recently detained in the Moscow-backed separatist region of South Ossetia during the eighth round of talks since Russia and Georgia fought a brief war there in August 2008.

Despite the spat, delegations from the two countries as well as from South Ossetia and another breakaway region Abkhazia, will hold their ninth round of talks on January 28, 2010, the international co-chairs said in a statement.

- The general assessment of this meeting has been once again a useful meeting, a difficult meeting - said Johan Verbeke, special representative of the UN Secretary-General.

Verbeke explained that the meeting was tough not least because - the participants have had the courage to put difficult issues on the agenda. -

- It was a difficult discussion in terms of having to build bridges between positions which at this stage remain apart - he added.

The United Nations, the European Union, and the Organization for Security and Cooperation in Europe (OSCE) are overseeing the talks.

The issue of detentions of Georgians by South Ossetia featured highly particularly in the first half of the talks, Georgian First Deputy Foreign Minister Giorgi Bokeria claimed.

- The discussions were dominated by the issue of the detention and kidnapping of Georgian citizens - Bokeria told journalists after the meeting.

Four Georgian youths, aged 14 to 17, were arrested in South Ossetia's main city Tskhinvali allegedly armed with grenades and other explosives last week, according to the separatist region's administration.

They have been charged with carrying explosives and crossing the border illegally.

Georgia has accused the separatist administration of "kidnapping" the boys from a village near the de facto border with South Ossetia.

Earlier Wednesday, Georgia also accused Russian forces of "kidnapping" five Georgian citizens off the Black Sea coast near another Russian-backed breakaway region, Abkhazia.

Tensions remain high between Georgia and Russia some 15 months after their war, with Moscow and Tbilisi regularly trading accusations.

On Tuesday, Russia's top military commander accused Georgia of re-arming.

Nikolai Makarov, chief of the Russian armed forces' general staff, was quoted by news agencies as saying arms sales to Georgia meant the country's military was better armed now than during the August 2008 war.

The Geneva Discussions are aimed purely at preventing renewed violence over the Russian-backed rebel regions, and easing humanitarian pressures over refugees and water supplies and movements of local inhabitants.

So far, they have drawn up a security mechanism for the prevention of incidents, based on meetings every fortnight between Russian and Georgian security forces as well as representatives from the two rebel regions.

But that deal got off to a shaky start, while key agreements on the non-use of force along the borders were examined for the first time during Wednesday's round of talks, the mediators said.

The talks have also failed so far to move far with the controversial issue of help for an estimated 30,000 displaced people.