The subject of the so-called sectoral missile defense has been taken off the agenda of Russian-NATO negotiations, a source in the Russian delegation said on Friday.

NATO has never given any encouragement to the Russian proposal, whereby a particular country or group of countries would be responsible for a specific missile defense sector - for instance, Russia shooting down a missile in its airspace targeting an alliance member.

"The idea of zonal missile defense? Its no longer under consideration. Thats it," the official said.

Russian Foreign Minister Sergei Lavrov said as much at the Russia-NATO Council meeting in Sochi on July 4, stating that the two sides were not able to reach an agreement on a sectoral missile defense system in Europe.

With the genuinely joint approach apparently off the table, it is not clear what the two sides have left to discuss.

In rejecting the zonal option, NATO member states cite their mutual defense obligations under the alliances founding Washington Treaty, which may not be delegated to non-members.

Russia and NATO agreed to cooperate on the European missile shield during the NATO-Russia Council summit in Lisbon in November 2010.

NATO insists there should be two independent systems that exchange information, while Russia favors a joint system with full-scale interoperability.

Russia has retained staunch opposition to the planned deployment of U.S. missile defense systems near its borders, claiming they would be a security threat. NATO and the United States insist that the shield would defend NATO members against missiles from North Korea and Iran and would not be directed at Russia.

Russia also demands legally binding guarantees that NATO missile defense systems will not be directed against it.