Even as Russia pledged to begin withdrawing its forces from neighboring Georgia on Monday, American officials said the Russian military had been moving launchers for short-range ballistic missiles into South Ossetia, a step that appeared intended to tighten its hold on the breakaway territory.

The Russian military deployed several SS-21 missile launchers and supply vehicles to South Ossetia on Friday, according to American officials familiar with intelligence reports. From the new launching positions north of Tskhinvali, the South Ossetian capital, the missiles can reach much of Georgia, including Tbilisi, the capital. ....