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Czarek Sokolowski, Associated Press
Military personnel poses in front of a NATO unmanned drone outside PGE National Stadium, the venue of the NATO Summit, prior to the official opening of the NATO summit in Warsaw, Poland, Friday, July 8, 2016.

WARSAW, Poland — Leaders of the NATO military alliance gathered Friday to order ambitious actions against a daunting array of dangers to the security of their nations and citizenry, including a rearmed and increasingly unfriendly Russia to Europe's east and violent Islamic extremism to the south.

"The decisions we're going to take together will once again confirm that Europe and North America stand together, act together to support all allies against any threats," NATO Secretary-General Jens Stoltenberg said, predicting a "landmark summit" meeting of U.S. President Barack Obama and other heads of state and government.

In an op-ed published in the Financial Times, Obama called Friday on NATO to stand firm against Russia, terrorism and other challenges, and to "summon the political will, and make concrete commitments" to strengthen European cooperation after the British people's vote in June to leave the European Union.

Stoltenberg said for NATO's 28 member nations to be safe, they don't only need to reinforce their own armed forces, but to come to the aid of partner nations in the Middle East and North Africa menaced by extremist violence.

"For our nations to be safe, it's not enough to keep our defenses strong, we must help to make our partners stronger," NATO Secretary-General Jens Stoltenberg said.

"Training local forces is often our best weapon against violent extremism," Stoltenberg told a pre-summit forum of defense and security experts. Among the items on the NATO meeting's ambitious agenda is increased assistance for Iraq's military, extension of the West's financial commitment to the Afghan military and police, aid for Tunisia, and getting NATO more involved in the campaign against Islamic State by authorizing use of AWACS surveillance planes to assist the U.S.-led coalition fighting the group.

In Warsaw, NATO heads of state and government will also order deployment of multinational units on the alliance's eastern frontiers — a move vigorously opposed by the Kremlin, but that Germany's defense minister said Friday is proper to counter what she called a "completely unpredictable and aggressive Russia."

Ursula von der Leyen said Poland and the Baltic states want greater protection because Russia's 2014 annexation of Crimea from Ukraine shows Moscow "doesn't respect borders." She told German broadcaster ARD that NATO must maintain a dialogue with Russia, but from a "position of strength."

"It's important that NATO deploys with such strength that it's clear nobody can see an advantage in attacking this military alliance," the German minister said.

As Obama and the other alliance heads of state and government were gathering in the Polish capital, a spokesman for Russian President Vladimir Putin said Moscow is willing to cooperate with NATO, even though he said it acts toward Russia like an enemy.

Russia "has always been open for dialogue" with NATO, especially to fight what it sees as a "genuine threat" — terrorism, Dmitry Peskov said.

"Russia is not looking (for an enemy) but it actually sees it happening," Peskov told reporters in Moscow., "When NATO soldiers march along our border and NATO jets fly by, it's not us who is moving closer to the NATO borders."

Warsaw may become the most highly secured city in the world during the summit, which takes place after a string of recent extremist attacks across the globe.

Helicopters hovered Friday above the National Stadium, the meeting's venue, while 6,000 police officers, backed up by soldiers, gendarmes, firefighters and other security officials, were out on Warsaw's streets.

Security efforts are most heavily concentrated at the stadium, which has been encircled by a metal barrier, and high around hotels hosting the many VIPs. Many streets in the city of 1.7 million have been blocked and some mass transit routes altered, inconveniencing many residents.

The airspace over Warsaw is also being monitored closely, with a ban on flights in a 100-kilometer (60-mile) radius from the stadium. Violators run the risk of being shot down.

Vanessa Gera in Warsaw and Nataliya Vasilyeva in Moscow contributed.