National park police officers are investigating how a banner reading "Refugees Welcome" got on to the Statue of Liberty Tuesday afternoon.

The banner, measuring about 3 feet by 20 feet, was unfurled atop the pedestal of the Statue of Liberty just before 1 p.m., according to the National Park Service.

It was affixed by nylon rope to the wall of the public observation deck at the base of the statue, according to the NPS. Rangers took it down more than an hour later.

Attaching banners to national monuments is prohibited. The United States Park Police is working to identify the suspects.

Someone running a social media account named Alt Statue of Liberty has claimed responsibility for the stunt. A person using the same email told NBC 4 New York, "We have no formal group -- just private citizens who felt like we needed to say something about the America we believe in."

The stunt happened the same day the Homeland Security Department announced expanded immigration enforcement policies.

Alt Statue of Liberty said in the email to NBC 4, "Speaking personally -- my grandparents met in a refugee camp after WWII, and my mother immigrated. So this touches close to home. But almost every American knows an immigrant or a refugee. We wanted to send a reminder about America when we're at our best -- the country that's a beacon of freedom to the world, built by immigrants. Walling off countries or entire religions is against our values."

The Statue of Liberty has regularly been invoked in the national discussion about immigration, particularly after President Trump instituted a federal travel ban barring nationals from seven Muslim-majority countries. An appeals court has refused to reinstate the executive order.