GENEVA, March 13 (Reuters) - Tens of thousands of Georgians who fled last year's war with Russia in breakaway South Ossetia will probably not be able to go home unless a political solution to the conflict is found, a U.N. expert said on Friday.

Walter Kaelin, the U.N. Secretary-General's representative on the human rights of internally displaced persons, said those who could not return to their homes for the foreseeable future were entitled to safety, housing and livelihoods.

"I am concerned that tens of thousands remain displaced and will probably not return to their homes in the Tskhinvali region/South Ossetia and adjacent areas unless solutions to the underlying conflict can be found," Kaelin told the United Nations Human Rights Council in Geneva.

He said that humanitarian access to the area had been "politicised by both sides," a problem that prevented him from visiting South Ossetia during a trip to Georgia in October.

Goran Lennmarker, a European special envoy on Georgia, said last month that there had been "de facto ethnic cleansing" in South Ossetia.

Russia invaded Georgia last August to thwart an attempt by Tbilisi to re-establish control over the pro-Russian breakaway region of South Ossetia, which has since declared independence along with another breakaway enclave, Abkhazia.

Since the five-day war, both regions have been recognised by Russia as independent states, secured by Russian troops.

Giorgi Gorgiladze, Georgia's ambassador in Geneva, told the Council it was unacceptable that Russia was "blocking" the access of international humanitarian aid.

Kaelin said the biggest challenge was integrating nearly a quarter of a million people uprooted by ethnic conflict in Georgia soon after the break-up of the Soviet Union.

"My biggest concern in Georgia is the fate of 220,000 people or more who had been displaced in the early 1990s because they remain largely forgotten and marginalised," he told reporters.

Housing conditions for this group were "unacceptable", but they deserved equal treatment, according to the Swiss expert.

He said he hoped the next session of talks between Georgian and Russian officials in Geneva -- co-chaired by the United Nations, European Union and Organisation for Security and Cooperation in Europe -- would resolve the sensitive question of humanitarian access. Dates for those talks have not been set. (Reporting by Stephanie Nebehay; editing by Mark Trevelyan)