(Updates with secretary-general statement)

By Louis Charbonneau

UNITED NATIONS, Aug 9 (Reuters) - U.N. Secretary-General Ban Ki-Moon is alarmed by intensified fighting in Georgia and worried about the violence spreading, his office said on Saturday evening.

Ban urged an immediate end to hostilities and a peaceful solution to the conflict, it said in a statement.

"The secretary-general is alarmed by the escalation of hostilities in Georgia which have resulted in large numbers of casualties and massive destruction in South Ossetia and other regions of Georgia," the statement said.

Ban was "profoundly concerned over mounting tensions in the Abkhaz zone, including the bombing of the Upper Kodori Valley." The statement called for maximum restraint and urged that the safety of unarmed U.N. military observers be guaranteed.

Russian troops and tanks rolled into former Soviet republic of Georgia on Friday after Georgian forces began an assault on the capital of the breakaway region of South Ossetia, which wants to become part of Russia.

Russia's military action dramatically intensified its long-running standoff with Georgia that has sparked alarm in the West and led to angry exchanges reminiscent of the Cold War.

Earlier Saturday, U.N. assistant secretary-general for peacekeeping Edmond Mulet said there have been "very substantial numbers of casualties, refugees and destruction" in Georgia.

Mulet told the U.N. Security Council that the Abkhaz authorities had asked him to withdraw U.N. military observers, known as UNOMIG, from the Upper Kodori Valley in Abkhazia but had declined to give him a reason.

Mulet said the observers were now at their base in the Abkhaz capital of Sukhumi to avoid getting caught in any cross-fire between Georgian and Abkhaz separatist troops.

Russian Ambassador Vitaly Churkin said he had no information about what was going on in Abkhazia.

Pro-Western Georgia earlier called for a cease-fire after Moscow's bombers widened an offensive to force Tbilisi's troops back out of the region in the Caucasus mountains.

Moscow says its military was responding to a Georgian assault to retake South Ossetia and has launched a peacekeeping operation to protect civilians. Russia backs the separatists who have controlled the regions since a war in early 1990s.

Inside the closed-door council meeting, Churkin compared Russian's operation in South Ossetia to the 1999 NATO operation in Kosovo, diplomats said. Speaking to reporters, he accused the Georgians of committing genocide and ethnic cleansing.

'OUT OF CONTROL'

U.S. Deputy Ambassador Alejandro Wolff made it clear Washington blamed Russia for escalating the fighting.

"This is a conflict that is expanding and getting out of control," he said. "The proximate cause is the massive escalation perpetrated by outside forces."

The members of the U.N. Security Council tried to agree on an appeal for a cease-fire but negotiations broke down because Russia has refused to pull its troops back to where they were on Aug. 6 and insists on occupying South Ossetia.

Britain's deputy ambassador, Karen Pierce, told Reuters Russia was demanding assurances that Georgian troops would stop fighting and pull out of South Ossetia but had refused to give any assurances they would do the same.

"The Georgians have made an offer of a cease-fire and it's concerning that the Russians won't respond to that," she said.

"It's clear that the Russians are looking to prolong the conflict in some way, because they will give no assurances, either about a cessation of hostilities or about withdrawing their forces."

Wolff made clear he believed Russia bore much of the responsibility.

The Security Council may discuss the crisis again on Sunday. (Additional reporting by Doina Chiacu in Washington)

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