BRUSSELS — Alarmed by the speed and scale of Russia's intervention in Syria, Western officials said Thursday that they had stepped up military exercises and deployed a small number of logistics personnel in Eastern and Central Europe.
Britain announced that it would send soldiers to the Baltic countries, Poland and Ukraine after the show of force by Russia's president, Vladimir Putin. Germany condemned Russia's operations in Syria in unusually pointed terms. NATO expressed alarm about Russia's incursions into Turkish airspace and the widening of the field of conflict to include the firing of cruise missiles from warships in the Caspian Sea.
"We are implementing the biggest reinforcement of our collective defense since the end of the Cold War," NATO's secretary general, Jens Stoltenberg, said before a meeting of defense ministers here Thursday. After the meeting, he said, "All of this sends a message to NATO citizens: NATO will defend you, NATO is on the ground, NATO is ready."
NATO has stationed Patriot batteries in Turkey to protect it from missiles emanating from Syria, but those had been scheduled to be removed this year. NATO officials have been considering whether to keep the batteries in Turkey, given Russia's actions, but Stoltenberg played down that possibility.
British officials said that units of up to 150 personnel would be regularly deployed to the Baltic countries, Poland and Ukraine to support military training. Michael Fallon, the British defense secretary, called the decision part of a "policy of persistent presence and aid for our allies on the eastern flag of NATO in response to Russian aggression and provocation."
The NATO moves in many ways are mostly symbolic, although Russia quickly reacted to the British announcement. Dmitry S. Peskov, a spokesman for Putin, told journalists that any increased presence of British troops in Eastern Europe would be regrettable, according to Agence France-Presse, adding that it would amount to Britain's using an alleged Russian threat as camouflage to press ahead with NATO expansion. Russia, he said, would respond with "parity."
As Western defense ministers — including the U.S. defense secretary, Ash Carter — met here on Thursday, much of the discussion focused on Russia and Syria, and in particular the timing of the launch of 26 cruise missiles across more than 900 miles, from the Caspian Sea, into Syria. "They did this the day before a meeting of NATO defense ministers," one NATO official said, speaking on the condition of anonymity because of the delicate nature of the negotiations. "Obviously that is a message, but who can say what Putin is thinking."
But even as the alliance sought to project its power toward the Russian border, and to remind Moscow that Russian maneuvers in Turkish airspace could invite a response, several NATO officials expressed frustration that they did not see a clear path out of the increasingly complicated tangle that has become NATO's relationship with Russia. One said that the expansion of NATO toward Russia's borders was the reason Putin was now maneuvering for elbow room, both in Eastern Europe and in trying to retain his access to the Mediterranean Sea through Syria.
Russia's aerial bombings in Syria and its support for a ground offensive there, which appeared to be an effort involving Iran, the Lebanese militia Hezbollah and the pro-government army, which is loyal to Syria's embattled president, Bashar Assad. Putin insists that Russia's intervention is intended to target militants from the Islamic State, but Western officials say he is using that pretext to batter other insurgent groups that have been trying to overthrow Assad.
"The Russians are not mainly targeting ISIS, but they are targeting other opposition groups and they are supporting the regime," Stoltenberg said. "And I call on Russia to play a constructive and cooperative role in the fight against ISIS, not to continue to support the Assad regime. Because to support the regime is not a constructive contribution to a peaceful and lasting political solution in Syria."
Bloomberg News quoted the German defense minister, Ursula von der Leyen, as saying, "When Russia attacks those who are fighting the Islamic State, that strengthens the Islamic State."
NATO announced that it was stepping up military exercises and establishing two small military headquarters, in Hungary and Slovakia, supplementing six others — in the Baltic nations of Estonia, Latvia and Lithuania, and in Bulgaria, Poland and Romania. Each headquarters has about 80 military personnel, about half from the host state and the rest from NATO, according to officials at the alliance in Brussels. These officials said the headquarters mainly served as hubs for planning for potential reinforcement by NATO forces and assessing logistics, like the depths of ports or the lengths of runways.
Meeting separately in Luxembourg, European Union interior ministers on Thursday were seeking to address the region's migration crisis that has been prompted in part by the Syrian conflict.
The ministers were discussing a common rule book for expelling migrants ineligible for asylum; ways to fortify the European Union's external borders; and a list of safe countries where migrants can be returned.
The ministers' conclusions are likely to be discussed at a summit meeting of European Union leaders on Oct. 15 and 16, when the issue of migration will top the agenda.
Arriving at the meeting in Luxembourg, Theresa May, the British home secretary, called for urgent measures to dissuade migrants unlikely to qualify for asylum from going on dangerous journeys to Europe.
"We should be sending economic migrants back to their countries of origin," May told reporters. "On returns, we need to see Europe upping its game."
Jean Asselborn, the foreign minister of Luxembourg who is leading the meeting, told reporters, "The control of external borders, immigration generally and also returns — it's a package."