BRUSSELS (AP) ― NATO announced Tuesday that it will deploy Patriot anti-missile systems near Turkey’s southern border, shoring up defenses against the threat of cross-border attacks from Syria and bringing the United States and its allies closer to Syria’s civil war.

The alliance’s 28 members decided to limit use of Patriots solely for the defensive purpose of warding off the mortar rounds and shells from Syria that have already killed five Turks. But the announcement also appeared to be a message to Syrian President Bashar Assad’s regime at a time when Washington and other governments fear Syria may be readying its chemical weapons stockpiles for possible use.

“We stand with Turkey in the spirit of strong solidarity,” NATO Secretary-General Anders Fogh Rasmussen told reporters. “To anyone who would want to attack Turkey, we say, ‘Don’t even think about it!’”

Fogh Rasmussen stressed that the deployment of the Patriot systems ― which includes missiles, radar and other elements ―wouldn’t be a first step toward a no-fly zone over parts of Syria or any offensive operation against the Arab state.

But the decision to deploy the systems takes the U.S. and its European partners closer to the war, with the possibility of U.S.-made and NATO-operated hardware being used against the Assad regime for the first time.

Officials say the Patriots will be programmed so that they can intercept only Syrian weapons that cross into Turkish airspace. They aren’t allowed to penetrate Syrian territory preemptively. That means they would have no immediate effect on any Syrian government offensives ― chemical or conventional ― that remain strictly inside the country’s national borders.

Still, Fogh Rasmussen insisted that the weapons could help de-escalate tensions along a border across which tens of thousands of Syrian refugees have fled and which has emerged as a critical transit point for weapons being smuggled to the rebels fighting to overthrow Assad.

Germany and the Netherlands are expected to give Turkey several batteries of the latest PAC-3 version of the U.S.-built Patriots air defense systems, which intercepts incoming missiles. The U.S. would likely fill any gaps, possibly by sending some from its stocks in Europe.

But the exact details of the deployment and the number of batteries are still to be determined by NATO. A joint team is studying possible basing sites in Turkey, and parliaments in both Germany and the Netherlands must then approve shifting the assets and the possible involvement of several hundred soldiers.

It’s unclear if any American soldiers would need to be deployed.

Due to the complexity and size of the Patriot batteries ― including their radars, command-and-control centers, communications and support facilities ― they cannot be flown quickly by air to Turkey and will probably have to travel by sea, alliance officials said. They probably won’t arrive in Turkey for another month, officials predicted.

NATO, like the U.S., doesn’t want to be drawn into the Syrian conflict. Washington has refused to entertain proposals for no-fly zones over Syria or for providing military support to Syrian rebels, fearful of making the conflict even more violent after 21 months in which more than 40,000 people have died.

The U.S. also cites the risk of extremists among the rebels getting their hands on weapons that they may later use against U.S. allies such as Israel.

NATO previously installed long-range Patriot batteries on Turkish territory during the 1991 and the 2003 Iraq wars. They were never used and were withdrawn a few months later.

The Patriot, which first entered service three decades ago, has been successively upgraded over the years. Although mostly used for anti-aircraft defense, advanced versions can also be used against cruise missiles and against medium- and short-range ballistic missiles. They have a maximum range of about 160 kilometers and can reach altitudes of about 80,000 feet.

Syria is reported to have an array of artillery rockets, as well as short- and medium-range missiles. These include Soviet-built SS-21 Scarabs and Scud-B missiles. The Scuds are capable of carrying chemical warheads.

At NATO headquarters in Brussels, U.S. Secretary of State Hillary Rodham Clinton and the alliance’s 27 other foreign ministers “unanimously expressed grave concerns about reports that the Syrian regime may be considering the use of chemical weapons,” according to Fogh Rasmussen.

“Any such action would be completely unacceptable and a clear breach of international law,” he said.

His comments came a day after President Barack Obama warned of consequences if Assad made the “tragic mistake” of deploying chemical weapons. American officials say the U.S. and its allies are weighing military options in light of intelligence reports showing the Syrian regime may be readying its unconventional weapons and may be desperate enough to use them.

German ambassador Martin Erdmann said the Bundestag will probably take up the matter next week.

The decision was announced after the NATO foreign ministers met Tuesday with their Russian counterpart Sergey Lavrov. The Kremlin has stymied more than a year of international efforts to apply global pressure on the Assad regime, its strongest ally in the Arab world, but officials say it has expressed equal concern about the threat of any chemical weapons.

Speaking to reporters, Lavrov said Russia wouldn’t object to the Patriots.

“We are not trying to interfere with Turkey’s right” to defend itself, he said. “We are just saying the threat should not be overstated.”

Lavrov stressed that Syrian artillery strikes into Turkey were accidental. And he warned that the conflict “is being increasingly militarized,” and that more weaponry in the area would only add to that problem.

Addressing Lavrov and the other 27 NATO foreign ministers, Clinton said Washington and Moscow still have major differences on the political transition needed in Syria. She and her NATO partners issued a statement later, also stressing that the Patriots “will in no way support a no-fly zone or any offensive operation.”

Turkey, one of the harshest critics of the Assad regime, asked for the Patriots to defend against possible retaliatory attacks by Syrian missiles. It welcomed the NATO decision, adding in a government statement that it would press on with efforts “to solve the Syrian crisis through peaceful ways, with the same resolve as before.”

Turkey and Syria share a porous, 911-kilometer border, which has allowed rebel leaders to take shelter in Turkey and brought the countries to near war in recent months. Syria was blamed for shooting down a Turkish plane and for lobbing mortars that killed two women and three children.

Syria, which is party to the 1925 Geneva Protocol banning chemical weapons in war, has repeatedly insisted it would not use them even if it did possess such weapons.