Russian border guards said Saturday they have begun defending the de facto borders between Georgia and its two breakaway regions. The deployment quickly followed the signing of a deal that formalized Russia's control over the borders of South Ossetia and Abkhazia, the regions at the center of last summer's brief war. Russia has kept thousands of troops in the two regions since the fighting, including in border areas. The US and European Union consider this a violation of the cease-fire, which called for all troops to be pulled back to positions held before the war. The deployment of border guards - who fall under the command of the Federal Security Service, the main successor to the KGB - came just days before the start of NATO exercises in Georgia.