The countries of the former Soviet Union, along with Finland and Mongolia, participate in a Russian gauge-compatible network, using SA3 couplers. Major lines are electrified. Russia's Trans-Siberian Railroad connects Europe with Asia, but does not have the clearances needed to carry double-stack containers. Numerous connections are available between Russian-gauge countries with their standard-gauge neighbors in the west (throughout Europe) and south (to China, North Korea, and Iran via Turkmenistan). While the USSR had important railway connections to Turkey (from Armenia) and to Iran (from Azerbaijan's Nakhchivan enclave), these have been out of service since the early 1990s, since a number of frozen conflicts in the Caucasus region have forced the closing of the rail connections between Russia and Georgia via Abkhazia, between Armenia and Azerbaijan, and between Armenia and Turkey.