Muslim US Congresswoman Ilhan Omar apologized for her criticism of the pro-Israel lobby after dozens of her fellow lawmakers denounced her remarks as anti-Semitic.

"Anti-Semitism is real and I am grateful for Jewish allies who are educating me on the painful history of anti-Semitic Tropes", Omar said. "This is why I unreservedly apologize".

Omar became the center of a controversy after she tweeted on Sunday, "It's all about the Benjamins baby", using slang for a $100 bill in a message suggesting that US support for Israeli had been purchased through groups such as the American-Israel Public Affairs Committee (AIPAC).

Her comments were roundly condemned by members of Congress, many of whom, including House Speaker Nancy Pelosi, called on her to issue an apology for remarks they said were prejudiced and anti-Semitic.

Though Omar apologized, she maintained her position that groups such as AIPAC, the National Rifle Association and the fossil fuel industry exercise undue influence in Congress. 

"It’s been going on too long and we must be willing to address it," she said.

Omar's tweet sparked outrage in Congress, especially among fellow Democratic lawmakers, who began circulating for signatures a letter of protest to the House of Representatives leadership.

The latest criticism of Omar came less than a month since the congresswoman apologized for previous anti-Semitic comments.