An Islamic center in Madera, CA, was vandalized Tuesday with a sign that read, "No temple for the god of terrorism at Ground Zero."
Another sign read, "Wake up America, the enemy is here."
Both signs were signed by ANB, which stands for the American National Brotherhood, a group local authorities said they were not aware of.
It is the third attack on the center within a week, with another sign left last week and a brick thrown at a window at the center on Sunday.
Authorities are treating the incidents as hate crimes.
The proposed mosque and Islamic center on Park Place in lower Manhattan, about two blocks from Ground Zero, has sparked controversy across the nation, contributing to protests against mosques in Tennessee, Kentucky and California, as well as New York City.
In the recent primary campaigns in Florida, opposition to the New York mosque was voiced several times, and people running for elected office in New York are slated to speak at an anti-mosque rally near Ground Zero on the ninth anniversary of the 9/11 terrorist attacks.
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Also in New York City, on Tuesday night, a 21-year-old film student stabbed a cab driver after the driver, when asked, said he was a Muslim. There was no mention of the proposed mosque during that attack, according to police. The attacker is charged with attempted murder.
Last night, in Astoria, Queens, a drunken man barged into a mosque during prayer service, shouted anti-Muslim slurs and urinated on a prayer rug.
"When you have the level of anti-Muslim hate rhetoric that we are now experiencing - on the radio, over the Internet - these sorts of incidents are inevitable," said Ibrahim Hooper, spokesman for the Council on American-Islamic Relations. "The daily diatribes against Islam, especially regarding the manufactured controversy about the planned center in lower Manhattan, are triggering certain unstable individuals to perform these violent acts."
Many people opposed to the mosque being near Ground Zero have repeatedly said that they are not anti-Muslim, but feel that having the building so close to where nearly 2,800 people died at the hands of Muslim extremists is insensitive to the victims' families.
Other opponents of the mosque do not bother to make such distinctions, like those with images of the burning towers on their pickup trucks and the words "All I ever needed to know about Islam I learned on 9/11."
"What do Muslim Americans tell their children?" Hooper said. "What do you say when every day they see their faith maligned and they read of violent attacks? Has the hatred peaked? Is it going to get worse? I don't know. But it is getting scary out there."