PARIS  - The United States, Georgia's strongest ally and military trainer, on Sunday warned Russia to end aggression in the Caucasus or face a diplomatic head-to-head with Washington. The unspecified threat came as UN observers in Georgia confirmed that a military airport near Tbilisi was bombed and another former Soviet satellite state in Poland, a major US ally which is already a Nato partner, called for an EU stabilisation force to be sent in. "We have made it clear to the Russians that if the disproportionate and dangerous escalation on the Russian side continues, that this will have a significant long-term impact on US-Russian relations," Jim Jeffrey, Deputy National Security Advisor, told reporters in Beijing. Jeffrey added that Georgian troop withdrawal would provide a "test" of Russia's intentions. Poland called for EU forces to enter the embattled south Caucasus region as the bloc's foreign ministers prepare to meet in Brussels on Wednesday to determine its response to the crisis. "The European Union is prepared to play a role in stabilising this region on condition that the parties involved in the conflict cool down their emotions and end this escalating conflict," said Polish Foreign Minister Radoslaw Sikorski. Due to fighting between Georgian and Russian forces over Georgia's breakaway South Ossetia region, which has spread to another renegade province, Abkhazia, Sikorski said it was no longer possible for Russian soldiers alone to assure the peace. German Chancellor Angela Merkel called for an "immediate and unconditional ceasefire," in a telephone call with French President Nicolas Sarkozy. France holds the rotating European Union presidency and Merkel's spokesman Thomas Steg said: "The chancellor and President Sarkozy agreed to continue closely coordinating on the issue." French Foreign Minister Bernard Kouchner - who cited the strategic importance of a major oil pipeline in the region - warned in an interview of a Balkan-like spiral of violence, as he left Sunday on a mission to mediate in the conflict between Tbilisi and Moscow. "This reminds me all too much of other recent conflicts that have torn our continent apart, particularly in the Balkans," Kouchner told Le Parisien newspaper as he prepared to leave for the region to mediate with Moscow and Tbilisi. "We are facing an escalation of violence" that is "unacceptable at the doors of Europe", he said. Kouchner urged Russia to accept Georgia's offer to end hostilities, saying: "If one of the protagonists, which appears to be the case, commits to a ceasefire, the other one must do the same." During Angelus prayers in Italy, Pope Benedict XVI said his "most fervent desire is for military operations to cease and that, in the name of common Christian heritage, there be no reprisals that could deteriorate into an even bigger conflict." Nato Secretary-General Jaap de Hoop Scheffer on Sunday deplored the "disproportionate use of force" and Russia's lack of respect for Georgia's territorial integrity. Scheffer also urged an immediate ceasefire after Russian troops backed by tanks and fighter jets seized control of the breakaway Georgian province of South Ossetia. "The Secretary-General of Nato repeated today his call for an immediate ceasefire," a spokeswoman for the North Atlantic Treaty Organisation said. "He also expressed his concerns about the disproportionate use of force and lack of respect for the territorial integrity of Georgia," she added. The Nato is keen not to be drawn into the conflict.  "Nato does not have a mandate to play a direct role in the Caucasus," one Alliance official said.