(Corrects to paragraph 9 to show Rep. Tlaib is from Michigan, not Minnesota)

By Andrea Shalal and Andrew Hay

WASHINGTON (Reuters) -Muslim Americans and some Democratic Party activists say they will work to mobilize millions of Muslim voters to withhold donations and votes towards President Joe Biden's 2024 reelection unless he takes immediate steps to secure a Gaza ceasefire.

The National Muslim Democratic Council, which includes Democratic Party leaders from hotly contested states likely to decide the election, such as Michigan, Ohio and Pennsylvania, called on Biden to use his influence with Israel to broker a ceasefire by 5 p.m. ET (2100 GMT) on Tuesday.

In an open letter entitled "2023 Ceasefire Ultimatum," the Muslim leaders pledged to mobilize Muslim voters to "withhold endorsement, support, or votes for any candidate who endorses the Israeli offensive against the Palestinian people."

"Your administration's unconditional support, encompassing funding and armaments, has played a significant role in perpetuating the violence that is causing civilian casualties and has eroded trust in voters who previously put their faith in you," the council wrote.

Former U.S. Representative Keith Ellison, Minnesota's attorney general and the first Muslim elected to Congress, and Representative Andre Carson of Indiana are the organization's founding co-chairs.

The letter is the latest sign of growing anger and frustration in Arab and Muslim American communities about Biden's failure to condemn Israel's attacks on the Gaza Strip after an Oct. 7 attack by Hamas militants from Gaza that Israeli officials say killed 1,400 people and took 239 hostages.

Medical authorities in Gaza on Monday said 8,306 people, including 3,457 children, had been killed in Israel's three-week-old air and ground onslaught.

Israel Prime Minister Benjamin Netanyahu said on Monday he would not agree to any cessation of the attacks on Gaza. U.S. national security spokesman John Kirby said, "Hamas is the only one that would gain from that right now."

Representative Rashida Tlaib, a Palestinian American lawmaker from Michigan, on Monday released a 90-second video on X, the social media site formerly known as Twitter, decrying Biden's support of what she called "Israel's genocidal campaign in Palestine," adding "Don't count on our vote in 2024."

Basim Elkarra, executive director of the Sacramento Valley Council on American-Islamic Relations (CAIR), said Muslim votes could be crucial for Biden in his 2024 bid for a second term, noting that Michigan's 16 electoral votes were won by a narrow margin of just 2.6% in 2020.

Muslim Americans in Minnesota, where Biden plans to visit on Wednesday, last week issued a similar ceasefire ultimatum, with a noon Tuesday deadline. They said they planned a protest on Wednesday when the president visits their state.

Biden's reelection campaign had no immediate comment.

Biden hosted a meeting last Thursday with a handful of Muslim leaders, a White House official said, adding that administration officials continue to meet with Arab and Muslim community members concerned by Biden's handling of the crisis.

Although a self-described Zionist president, Biden has appointed more Arab Americans and Muslims to political posts than any predecessor, as well as the first two Muslim federal judges.

Jaylani Hussein, executive director of CAIR in Minnesota, said Muslim American leaders in other contested states that are crucial to Biden's 2024 reelection will make similar demands.

"We expect Wisconsin, Ohio and other states to do the same this week," said Hussein.

Hussein said he had no option but to vote against Biden in 2024 unless he called for fighting to stop. He said he was speaking as an individual, not on behalf of CAIR.

Around 70% of Muslim Americans backed Biden in 2020, Hussein said.

Muslim American community leaders in Michigan, Ohio and Wisconsin did not immediately respond to requests for comment.

Ahmet Tekelioglu, executive director of CAIR in Philadelphia, said Muslim Americans in the state were calling for an immediate ceasefire but he was not aware of plans to set a deadline.

(Reporting by Andrea Shalal in Washington and Andrew Hay in New Mexico. Editing by Heather Timmons and Howard Goller)