MOSCOW, February 26 (RIA Novosti) – Russian diplomatic sources have expressed optimism about a possible breakthrough in missile defense negotiations at Tuesday's foreign ministers’ meeting in Berlin, although their US counterparts were more reserved and said they expect no “major” breakthroughs, a respected Russian newspaper reported on the day of the talks.

The Kommersant daily, citing diplomatic sources on both sides, said Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry are likely to finally find common ground on missile defense at their first bilateral talks.

Missile defense has remained a key impasse in Russian-US relations in the past few years. Moscow has been irked by US plans to unilaterally deploy missile defense systems in Europe. NATO and the United States insist that the shield would defend alliance members against emerging missiles threats from North Korea and Iran, and would not be directed at Russia's nuclear deterrent.

Moscow has sought direct joint development and operation of any missile defense system, which NATO has declined.

Russian diplomatic sources told Kommersant a breakthrough could take the form of “political declarations at the highest level on principles of cooperation in the sphere of missile defense.” That would mean the two sides will seek to cooperate in the field of missile defense and refrain from using their potential against each other, the paper said.

Russia has also long sought such legal guarantees from NATO that any missile defense system will not be directed against Russia.

Diplomatic sources on both sides have confirmed “the parties have started discussing the possibility of drafting such documents,” the paper said.

To sign such an "executive agreement,” meeting the objectives of the US president, US President Barack Obama would not necessarily need to seek the approval of Congress. For his part, Russian President Vladimir Putin would only have to sign a memorandum of understanding, similar in concept to the US document, to clinch a deal.

A high-level US State Department official, however, said no “big breakthrough” was expected at Tuesday’s meeting, which he said will mainly focus on the Syrian crisis.

The official said Washington expects Russia could play a key role in convincing the Syrian regime that there needs to be a political transition, but there are no signs of major breakthroughs or change in the Russian position.

Russia has faced strong international criticism over its refusal to back UN sanctions against Syria, a major ally in the Arab world, over what it called the pro-rebel bias of some resolutions proposed by Western nations.

Moscow has consistently denied it is backing President Bashar al-Assad and says it is concerned that the Syrian president’s forced departure would only worsen the conflict.

Updated at 20:20 Moscow time; recasts first and second-to-last paragraphs.