ANALYSTS' VIEW - Tension mounts over Georgia

(Reuters) - Tension remained high in Georgia on Thursday, with Russian troops and armour moving around three towns inside the country and ignoring demands by Washington that Moscow respect its territorial integrity.

Moscow also clashed with Georgia's ally Ukraine over the movements of Russia's Black Sea fleet after Ukraine's president decreed Russian warships obtain permission before entering or leaving their base in the Ukrainian port of Sevastopol.

Following are comments from security, political and economic analysts:

MICHAEL COX, PROFESSOR OF INTERNATIONAL RELATIONS, LONDON SCHOOL OF ECONOMICS

"This is going to be a defining crisis in the United States-Russian relationship. The danger is that neither side feels it can back down.

"The Russian role in Georgia has massive implications for the Russian role in Ukraine and the Baltic republics. Not surprisingly, they are taking an increasingly strong line on this because they see this as a defining moment for their relationship with Russia.

"We may only be at the beginning of this crisis rather than in the middle or at the end of it.

"If this thing escalates we could possibly see differential relations within NATO -- we are at one of those crossroads. The last thing many European members of NATO would want would be a kind of showdown. They have very close relations. Russia is Europe's third largest trading partner. There is massive economic involvement between EU countries and Russia and many are energy dependent on Russia.

"They will not want to threaten that. On the other hand, the U.S. is taking a tougher line and so we could be heading -- not just for an increasing showdown with the U.S. and Russia which could get very nervy -- but we could also be leading to some very difficult discussions going on in backrooms between European countries and the Americans."