MOSCOW (AP) — The Kremlin says President Vladimir Putin has warned German Chancellor Angela Merkel of a threat to the gas supplies Russia sends to Europe via Ukraine.

Putin told Merkel in a telephone call Tuesday that Ukraine has been reluctant to sign a contract on Russian gas supplies for the coming winter and that it "threatens transit to Europe." Moscow has warned that Ukraine could siphon Russian gas intended for European consumers.

A pipeline through Ukraine is a major conduit for gas exports to Europe. Past disputes between Russia and Ukraine have led to cutoffs, including a 2009 standoff that caused serious disruptions in winter supplies.

Russia's annexation of Crimea and its support for separatist rebels in eastern Ukraine has brought relations between the two ex-Soviet neighbors to the verge of rupturing.