Updated

Israel ordered a special call-up of reserve troops Wednesday as nervous citizens lined up at gas-mask distribution centers, preparing for possible hostilities with Syria.

With the U.S. threatening to attack Syria over its alleged use of chemical weapons, Israel fears that Syria may respond by attacking Israel, a close American ally. While Israeli officials believe the chances of a Syrian strike remain slim, people were clearly preparing for the possibility.

Prime Minister Benjamin Netanyahu spent the day huddled with his top security advisers discussing the situation. Afterwards, he sent a mixed message, urging people to remain calm while also approving special precautionary measures.

"There is no reason to change daily routines," he said. "At the same time we are prepared for any scenario." He said the Israeli military "is ready to defend against any threat and to respond strongly against any attempt to harm Israeli citizens."

An Israeli official briefed on the meeting said the government had ordered a "limited" callup of reserve units to beef up civil defense preparations and to operate air-defense units near the border. Other officials briefed on the meeting said the call-up is anticipated to bring in "hundreds" of troops.

Earlier, defense officials had confirmed the deployment of Iron Dome and Patriot missile-defense batteries in areas near the Syrian border.

Israel uses U.S.-made Patriot missile defense batteries against medium-range missiles, and the Iron Dome system is designed to intercept rockets fired from short distances of up to 50 miles.

Israel says the Iron Dome system shot down one of the four rockets launched from Lebanon into northern Israel last week, and intercepted a rocket fired toward the Red Sea resort town of Eilat earlier this month. The Iron Dome system also has intercepted rockets launched from the Gaza Strip.

The defense officials said they believed the U.S. would carry out an attack on Syria within days, and that Israel would receive U.S. notification before any strike. All officials spoke on condition of anonymity because they were discussing confidential security assessments.

Large crowds gathered at gas-mask distribution centers across the country, waiting in long lines for protection kits.

Israeli demand for gas masks has tripled in recent days, said Maya Avishai of the Israeli postal service, which oversees gas mask distribution. About five million Israelis, roughly 60 percent of the population, now have gas masks, she said. All citizens are eligible for the kits.

A large crowd formed a Tel Aviv distribution center Wednesday, where Galia Cohen was among those waiting in line for hours to collect free masks for herself and her family.

"I have two children and I am afraid for my children," she said.

Sivan Yehieli, chairman of a civilian emergency response committee along Israel's northern border with Syria and Lebanon, told Army Radio that towns in the region were preparing for a possible attack, readying bomb shelters and drilling school children on how to flee to shelters.

"The citizens need to be prepared just like the army," said Yehieli. "We don't want to find ourselves surprised."

Despite the precautions, Israeli officials believe the chance of a Syrian attack remain slim. They believe that Syrian President Bashar Assad, bogged down in a civil war, has little desire to open a new front with Israel, especially after he has appeared to gain the upper hand back at home.

Israeli officials also believe that Syrian ally Hezbollah, a bitter enemy of Israel, does not want to go to war at the current time. Hezbollah has sent hundreds of fighters to back Assad's troops and is also preoccupied with domestic troubles at home in Lebanon.

On Tuesday, Netanyahu warned Syria that if Israel is targeted, it will respond "with force."

Israel and Syria are bitter enemies. But Israel has kept its distance from the Syrian civil war, in part because it does not want to get dragged into the conflict and also because many of the factions battling the Syrian regime are hostile to Israel.

More than 100,000 people have been killed in Syria. Violence has occasionally spilled over into the Israeli-controlled Golan Heights, where Syrian mortar shells have landed. Israel has occasionally accused Syria of aiming at Israeli targets, and Israeli troops have returned fire.