And in Philadelphia, Chicago, Washington and New York, foreign-looking taxi drivers were threatened, cursed and, in some cases, yanked from cabs and assaulted, according to the Washington-based Arab American Anti-Discrimination Committee and local religious leaders.
In several of the cases, including in Philadelphia, the drivers were neither Arab nor Muslim, but turban-wearing Sikhs from India.
"It's [against] anybody with darker skin, anybody who strikes somebody as a cartoon version of what an Arab might look like," said Hussein Ibish, spokesman for the Washington-based antidiscrimination group.
"And we're still in the shock and grief stage. We're not even in the anger phase yet. There's a reservoir of rage that has yet to fully develop, and I'm very afraid," Ibish said.
Several people drew a comparison to the attacks on and internment of Japanese Americans during World War II, calling on Americans not to react the same way today.
"Are we going after the perpetrators or are we targeting an entire faith and race?" asked Amin Elarbi, president of the Al-Aqsa Islamic Society, Philadelphia's largest mosque.
The incident in Lower Merion occurred about 3:30 a.m. A lone night-shift worker at a 7-Eleven on City Avenue heard a banging on the front door, which he had locked while mopping the floor, according to store manager Affan Hashmi.
When the worker, a Pakistani, opened the door, the man at the door pulled a gun, pointed it to the worker's head and made a threat that apparently included the word Arab, Hashmi said. The worker managed to call the Lower Merion police, and the assailant left.
From a surveillance video, police identified the man as an off-duty officer from the 19th Police District, just over the city line in West Philadelphia, a Philadelphia police official said on condition of anonymity.
The official said two off-duty officers may have been involved. Both allegedly had been drinking in Lower Merion before the attack.
Police Commissioner John F. Timoney reacted angrily to the report, saying: "It's disgraceful."
If the allegations prove to be true, Timoney said, "they will be dealt with as sternly as humanly possible, both criminally and administratively."
Deputy Police Commissioner John J. Norris, commander of the Internal Affairs Division, said both officers, on the force about a year, have been reassigned to desk duty.
Lower Merion police were investigating the incident and may file charges, officials from both departments said.
"If the officers are arrested, we will act on that," Norris said. "If they are not, we will continue our internal investigation to determine if any action is needed."
Elsewhere, Arab and Muslim organizations reported receiving dozens of threatening calls and e-mail messages, although none said it had closed its offices because of them.
In Colorado Springs, Colo., four men allegedly entered the city's only mosque, cursed at a worker, and threatened to burn down the building, according to a local Islamic Society spokesman.
Internet chat sites were filled with angry messages from all sides, some calling for deportation of all noncitizens from the Middle East and others pleading for restraint.
In South Jersey, two Collingswood businesses - both owned by Indians - were spray-painted during the night.
The words "Leave Now [expletive]" were painted across the facade of Pete's News Agency, one of the two businesses.
"I don't understand. What did I do wrong?" asked owner Dipak Bhuta, 42, a native of Bombay, India. "Our families didn't do anything. But because I come from another country they did this. . . . I've been a U.S. citizen for 14 years."
Collingswood Police Capt. Frank Woshnak said extra patrols had been deployed to watch the businesses.
In Voorhees, residents in the Heritage Grove development said they found anti-Jewish flyers tucked in their doors yesterday, including an essay by a purported Palestinian suicide bomber that read: "Get out of Palestine, Jews. Or die here."
It was signed by an organization called "The National Alliance."
The Philadelphia branch of the Anti-Defamation League said it was investigating an allegation of anti-Jewish comments made at a suburban public school.
"The children said it's the Jews' fault and we should be bombing Israel," said ADL regional director Barry Morrison, adding that the league was monitoring comments directed at all groups.
In Villanova, the Foundation for Islamic Education erected plywood sheets over its entrance sign as a precaution against vandalism, foundation director Mustafa Ahmed said.
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The Associated Press contributed to this article.