The Palestinian government has demanded its investigators are included in a probe into the killing of three Palestinian Americans in Chapel Hill, North Carolina, in an attack it described as "terrorism".
US police have charged Craig Seymour Hicks with the murder of his neighbours Deah Barakat, 23, Yusor Abu-Salha, 21, his wife, and her sister Razan Abu-Salha, 19, and said they were killed following a dispute over parking.
However, FBI investigators are also examining whether their Muslim faith played a role in Hicks' motivation.
Branding Hicks "an American extremist and hateful racist", the Palestinian Foreign Ministry said that there was a rising tide of Islamophobia in the US.
"We consider it a serious indication of the growth of racism and religious extremism which is a direct threat to the lives of hundreds of thousands of American citizens who follow the Islamic faith," the ministry said in a statement.
It called for "a serious investigation and the involvement of Palestinian investigators to clarify the circumstances of these assassinations and premeditated murders" in Chapel Hill.
It comes as the leader of the world's largest bloc of Muslim countries said the killings had exposed "rising anti-Muslim sentiments and Islamophobic acts in the US".
Iyad Madani Secretary General of the 57-nation Organisation of Islamic Cooperation, called on the US government to take steps to combat "stereotyping, discrimination and profiling" of Muslims.
On social media, Hicks had posted anti-religion comments and pictures of a firearm.
The family of the victims has demanded that the killings be treated as hate crimes, with many declaring their support under the hashtag #MuslimLivesMatter on Twitter.
"If it, for example, was a Muslim man who executed three Christians, white American students who were young and beautiful and had just gotten married what would the reaction be?"" asked Steve Sosebee, who heads the Palestine Children's Relief Fund, an aid organization that Barakat volunteered with in 2012.
On Friday, US president Barack Obama condemned the killings, and said that no-one in the US should be discriminated against over their religion.