The murder of sisters Razan Mohammad Abu-Salha, 19, and Yusor Mohammad, 21, along with Yusor's husband Deah Shaddy Barakat, 23, in North Carolina was a "dangerous sign of racism and religious extremism," Palestinian official Wafa news agency quoted the foreign ministry as saying.
The ministry said the shooting "directly threatens the lives of hundreds of thousands of Muslim Americans".
The sisters were Jordanian Americans of Palestinian origin, and Barakat's parents are immigrants from Syria of Palestinian descent.
He is charged with three counts of first degree murder.
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The murders are being investigated as a hate crime, and have sparked outrage among Muslims worldwide.
The Palestinian foreign ministry called the murder "terrorism, which targets civilians based on their religion," according to Wafa.
Demonstrations have been held throughout the Palestinian territories, especially the Gaza Strip, where further rallies are planned for next week.
US President Barack Obama condemned yesterday the "brutal and outrageous" execution-style murders of the three, saying no one in the US "should ever be targeted because of who they are, what they look like, or how they worship.