Gates arrived in Moscow today in a bid to persuade Russia to cooperate with the United States on plans to deploy parts of a missile-defense shield in Poland and the Czech Republic.
He invited Russia to participate in the shield as a partner.
Washington maintains the system aims at countering missile attacks from what it calls "rogue" states, such as Iran and North Korea. But Moscow says it threatens Russia.
Gates is scheduled to meet with President Vladimir Putin, First Deputy Prime Minister Sergei Ivanov, and other Russian officials.
Meanwhile, the head of the U.S. Missile Defense Agency, General Henry Obering, is in Prague today to discuss the anti-missile shield with Czech leaders.
(Reuters, AFP, ITAR-TASS)