The headquarters of a Washington-based Muslim advocacy group have been sent a page from the Quran smeared with what appears to be faeces along with a letter with an image depicting former US president Barack Obama as a monkey.
The Council on American-Islamic Relations (CAIR) said it had contacted the police after receiving the "racist, Islamophobic" letter from Michigan with what is thought to be a fake return address.
The apparent "foreign substance" appears on an English translation of the Quran and the letter shows the racist image of Obama.
CAIR, described as the largest Muslim civil rights and advocacy organisation, say the incident is in response to rising anti-Muslim sentiment in the US following the election of Donald Trump.
CAIR national executive director Nihad Awad said: "This is just a sample of the hate targeting American Muslims and other minority groups in the wake of the presidential election.
"These bigoted acts will never stop us from defending the civil rights and religious freedom of all Americans."
The group also condemned Trump's administration for what is described as "deafening silence" over what it described as a growing number of anti-Muslim incidents in recent days, including the targeting of mosques in Colorado, Florida, Ohio, Iowa, Kentucky and several other reported incidents.