WARSAW, Poland -- NATO members and partners on Monday launched their biggest ever joint exercise in Poland at a time when central and eastern European nations are seeking strong security guarantees amid concerns about Russia.

Polish Defence Minister Antoni Macierewicz and U.S. Ambassador Paul W. Jones opened the Anaconda-16 exercise during a ceremony in Warsaw. The exercise will involve some 31,000 troops from Poland, the U.S. and 17 other NATO member nations and from five partner nations, according to Poland's military Operational Command that is organizing and co-ordinating the exercise.

Some 12,000 of the troops are from Poland, almost 14,000 from the U.S. and some 1,000 from Britain, the Anaconda-16 press office said.

Russia says that any presence of NATO troops close to its borders is a threat to its security.

"We do not hide that we have a negative attitude toward the NATO line of moving its military infrastructure to our borders, drawing other countries into military unit activities," Foreign Minister Sergey Lavrov said in Moscow.

"This will activate the Russian sovereign right to provide its own safety with methods that are adequate for today's risks," he said.

Russia's military has talked about stationing its state-of-the art Iskander missiles in Russia's westernmost Baltic outpost of Kaliningrad, which borders Poland and Lithuania.

Poland, Lithuania and other nations in the region, as well as NATO leaders, are stressing that any military presence or exercises are purely defensive and deterrent measures focused on threats from the Middle East.

The drill is part of NATO's exercise program and is being held just weeks before NATO holds a crucial summit in Warsaw expected to decide that significant numbers of NATO troops and equipment will be based in Poland and in the Baltic states. Those countries are particularly concerned about the armed conflict in Ukraine, where Moscow supports the separatists, but other countries in the region, including Romania and Bulgaria, are concerned about Russia's activity and have also contributed troops to the exercise.

Anaconda-16 runs through June 16 on test ranges across Poland and will be formally closed by officials at a ceremony in Warsaw on June 17. It will train, exercise and integrate Polish command and troops with those of other allied nations in responding to military, chemical and cyber threats on land, sea and in the air.

Involved will be some 3,000 vehicles, 105 airplanes and helicopters, along with 12 Navy ships, the Operational Command said.

Preparations started Monday for an airborne operation the following day involving some 2,000 U.S., British and Polish paratroopers that will be the first action exercise on Anaconda-16's schedule. The next day, a multinational engineering battalion will build a temporary bridge across the Vistula River that some 300 vehicles are to cross on June 15.

The Anaconda exercise was initiated by Poland in 2006 and has gradually grown to include many other NATO members.

Alison Mutler in Bucharest contributed to this story