New Democratic congresswoman Ilhan Omar has apologised for tweets implying US lawmakers only support Israel because of lobby money.
She faced widespread condemnation for suggesting the American Israel Public Affairs Committee (Aipac) was buying influence for pro-Israel policies.
Republicans and Democrats alike said the tweets stoked anti-Semitic tropes about Jews and money.
The Minnesota lawmaker has previously been accused of anti-Semitism.
Ms Omar released a statement "unequivocally" apologising for her tweets on Monday, following an apparent conversation with Speaker of the House of Representatives Nancy Pelosi about the row.
"Anti-Semitism is real and I am grateful for Jewish allies and colleagues who are educating me on the painful history of anti-Semitic tropes," Ms Omar said.
"We have to always be willing to step back and think through criticism, just as I expect people to hear me when others attack me for my identity."
Ms Omar added that she still believes lobbyists are "problematic" in US politics - "whether it be Aipac, the NRA or the fossil fuel industry".
Listening and learning, but standing strong 💪🏽 pic.twitter.com/7TSroSf8h1— Ilhan Omar (@IlhanMN) February 11, 2019
What was the controversy?
In response to a tweet on Sunday from a journalist questioning why US political leaders always defend Israel, Ms Omar used a slang term for $100 bills, writing: "it's all about the Benjamins baby."
It's all about the Benjamins baby 🎶 https://t.co/KatcXJnZLV— Ilhan Omar (@IlhanMN) February 10, 2019
When challenged where she thought such money was coming from, the 36-year-old Somali-American tweeted back: "Aipac."
Aipac spends millions of dollars a year lobbying lawmakers and the US federal government to adopt pro-Israel policies, according to campaign-finance monitors.
Aipac's website says it offers a congressional club membership that requires "political contributions in a clearly pro-Israel context to candidates".
However, it is one of countless special interest groups in Washington DC that advocate on issues covering everything from abortion to gun control, unions, energy, defence, healthcare and beyond.
In response to Ms Omar, Aipac tweeted: "Our bipartisan efforts are reflective of American values and interests."
We are proud that we are engaged in the democratic process to strengthen the US-Israel relationship. Our bipartisan efforts are reflective of American values and interests. We will not be deterred in any way by ill-informed and illegitimate attacks on this important work.— AIPAC (@AIPAC) February 11, 2019
What's the context?
Ms Omar - who in November became one of the first two Muslim women elected to Congress - has been criticised before for criticisms of Israel.
She has come under fire for supporting the Boycott, Divestment and Sanctions movement (BDS), which seeks to isolate Israel economically to force it to change its policies towards the Palestinians.
Last month, Ms Omar apologised for saying Israel had "hypnotised" the world - a term once used by Nazis.
She said she had not been aware of the historical context.
What's the reaction?
Republicans have criticised Ms Omar over her latest controversy, but the backlash was just as intense from congressional members of her own party.
House of Representatives Speaker Nancy Pelosi and other Democratic leaders released a statement on Monday condemning the tweets and calling on Ms Omar to "immediately apologise for these hurtful comments".
"Legitimate criticism of Israel's policies is protected by the values of free speech and democratic debate that the United States and Israel share.
"But Congresswoman Omar's use of anti-Semitic tropes and prejudicial accusations about Israel's supporters is deeply offensive."
The statement was also signed by Majority Leader Steny Hoyer, Democratic Caucus Chair Hakeem Jeffries and vice-chair Katherine Clark, Majority Whip James Clyburn, and Assistant House Speaker Ben Ray Lujan.
Mrs Pelosi also indicated she had spoken with Ms Omar about the controversy.
Max Rose, a New York Democrat, called Ms Omar's remarks "deeply hurtful".
Congresswoman Omar’s statements are deeply hurtful to Jews, including myself. pic.twitter.com/u3f2JHESFA— Max Rose (@MaxRose4NY) February 11, 2019
House Judiciary chairman Jerry Nadler, also of New York, said Ms Omar's choice of words was "deeply disappointing and disturbing".
Elaine Luria of Virginia and Josh Gottheimer of New Jersey on Monday published a letter urging House leaders to "unite against anti-Semitism and hateful tropes and stereotypes".
The letter did not name Ms Omar, but said top Democrats must confront lawmakers who make "reckless statements".
Chelsea Clinton, daughter of former President Bill Clinton and former Secretary of State Hillary Clinton, tweeted: "We should expect all elected officials, regardless of party, and all public figures to not traffic in anti-Semitism."
Ms Omar later responded to Ms Clinton by saying she would be "happy to talk", adding "we must call out smears from the [Republican party] and their allies".
👋🏽 Chelsea - I would be happy to talk. We must call out smears from the GOP and their allies. And I believe we can do that without criticizing people for their faith.— Ilhan Omar (@IlhanMN) February 11, 2019
I look forward to building an inclusive movement for justice with you. 💪🏽 https://t.co/EGA9NQfBCi
House Republican leader Kevin McCarthy was quick to call for action against Ms Omar.
Anti-Semitic tropes have no place in the halls of Congress. It is dangerous for Democrat leadership to stay silent on this reckless language.— Kevin McCarthy (@GOPLeader) February 11, 2019
Mr McCarthy himself faced condemnation last year for a now-deleted tweet that suggested billionaire Jewish donors were attempting to "buy" the mid-term elections.