MOSCOW (AP) — Russian President Vladimir Putin, in a New Year's message to U.S. President Barack Obama, has called for cooperation between their countries to respond to international challenges.

Ties between Moscow and Washington reached a post-Cold War low when Russia annexed Ukraine's Crimean peninsula and threw its support behind separatist rebels in eastern Ukraine. The U.S. and other nations responded with economic sanctions against Russian officials, state-owned companies and entire sections of the economy.

The Kremlin on Wednesday quoted Putin's New Year's greetings to Obama as saying the "relations between Russia and the United States are crucial to ensuring global security."

Putin was also quoted as saying that both countries would "successfully take on new challenges and threats" across the world if they were to engage in a "constructive dialogue."