The two rival Palestinian factions have failed to heal their political disputes since Hamas fighters expelled Fatah from Gaza in a short war in 2007
Following the ceremony Viktor and Amalija Knavs' attorney Michael Wildes said the US president's in-laws had followed standard procedure in obtaining their citizenship.
"They have travailed a wonderful journey like most have, millions have, in getting citizenship and waiting the requisite period of time," Wildes said,
"We just thank everybody for their attention to this very important dialogue that we're having on immigration. This is an example of it going right," he added.
Melania Trump moved to the US in 1996 from Slovenia to pursue a career as a model and became a citizen in 2006.