GORI, Georgia — Explosions were heard near Gori on Thursday as a Russian troop withdrawal from the strategic city seemed to collapse. A fragile cease-fire appeared even more shaky as Russia's foreign minister declared that the world "can forget about any talk about Georgia's territorial integrity."

The declaration from Russian Foreign Minister Sergey Lavrov came simultaneously with the announcement that Russian President Dmitry Medvedev was meeting in the Kremlin with the leaders of Georgia's two separatist provinces.

"One can forget about any talk about Georgia's territorial integrity because, I believe, it is impossible to persuade South Ossetia and Abkhazia to agree with the logic that they can be forced back into the Georgian state," Lavrov told reporters.

The strategically located city is 15 miles south of South Ossetia, the separatist region where Russian and Georgian forces fought a brutal five-day battle. Russian troops entered Gori on Wednesday, after the two sides signed the cease-fire that called for their forces to pull back to positions they held before the fighting.

The first of two planned U.S. aid flights arrived in the Georgian capital of Tbilisi late Wednesday, carrying cots, blankets and medicine for refugees displaced by the fighting. The shipment arrived on a C-17 military plane, an illustration of the close U.S.-Georgia military cooperation that has angered Russia.

Besides the hundreds killed since hostilities broke out, the United Nations estimates 100,000 Georgians have been uprooted; Russia says some 30,000 residents of South Ossetia fled into the neighboring Russian province of North Ossetia.