US plans for a shield against potential missile attacks from Iran were a big factor in deteriorating relations with Russia during the administration of George W. Bush and have continued to strain improving ties under President Barack Obama. Moscow is demanding binding guarantees from the United States and NATO that the system would not threaten Russian security, a nonstarter in Washington because of strong opposition to any set restrictions on missile defenses.

Reaching a cooperation deal by May would be a big boost for relations, setting an upbeat tone at the outset of what is likely to be a new presidential term for Prime Minister Vladimir Putin.