Republicans have seized on the controversy, hoping to exploit divisions within the Democratic party and calling for Ms Omar to be removed from the Foreign Relations Committee.
In a tweet of his own, Donald Trump, the US president, called Ms Omar’s remarks “a dark day for Israel”.
Ms Omar, a Somali-American, said that she is raising legitimate questions about influence in Washington and she worries that anything she says about Israel and its treatment of Palestinians can be construed as anti-Semitic.
“Being opposed to (Prime Minister Benjamin) Netanyahu and the occupation is not the same as being anti-Semitic,” she tweeted on Sunday. “I am grateful to the many Jewish allies who have spoken out and said the same.”
It is at least the third time Ms Omar has forced older pro-Israel Democrats in senior positions into awkward territory over US-Israeli policy.
The controversy has presented a challenge for the Democratic leadership, torn between a need to admonish Ms Omar and appear in control of the newly elected progressive wing that is less willing to toe the party line.