Philadelphia police said Tuesday that they plan to step up patrols around city mosques as they search for whoever left a severed pig’s head outside one Sunday.

Police are also looking to enhance security footage that shows someone throwing the animal’s head out the passenger door of a red pickup truck, Commissioner Charles Ramsey said. No arrests have been made in the incident outside the Al Aqsa Islamic Society in west Philadelphia.

The Koran prohibits Muslims from eating pork, and pigs have often been used to taunt or offend Muslims. Last year, demonstrators in Greece left a pig’s head and painted anti-Muslim slogans outside Islamic studies center in Athens. Similar incidents have occurred in France as well.

Police told WTXF the incident is related to a harassing voicemail left on the mosque's answering machine the day after the Paris terror attacks.

“I said a prayer for the guy that may God put him on a straight path. If he was in the right mind, he wouldn’t be doing this,” manager Nabil Khalil told the Fox affiliate.

A caretaker told Philadelphia police he found the head near the door of the mosque when he arrived for work Monday morning. A day later, Mayor Michael Nutter pledged $2,000 reward for information leading to a conviction in any hate crime case.

Nutter took the opportunity to respond to GOP presidential candidate Donald Trump’s comments on banning Muslims from entering the U.S. They mayor suggested his city banish Trump instead.

"Trump is literally trying to radicalize Americans against Muslims, and that's not what America is about," Nutter said.

Nutter called Trump's proposal "flat-out ignorant" and said, "If I had the power, the only banning that would be done is that I would ban him from Philadelphia. We don't have any room for that kind of stupidity here."

On Monday, Trump proposed stopping Muslims from coming to America "until we are able to determine and understand this problem and the dangerous threat it poses." His suggested ban was quickly condemned by other presidential candidates from both parties. The mayor of St. Petersburg, Florida, tweeted earlier Tuesday that he also would ban Trump from his city.

The Associated Press contributed to this report.