The support for a boycott of Israel by the first two Muslim women in the US Congress has opened a breach in the Democratic Party and threatens to create a fissure in the ironclad US-Israeli alliance.

Ilhan Omar and Rashida Tlaib made their debut in the House of Representatives in January openly declaring their support for the Palestinian-led Boycott, Divestment, Sanctions movement, or BDS.

The movement launched more than a decade ago and modelled on the 1960s movement to pressure South Africa over apartheid, calls for people and groups to severe economic, cultural and academic ties to Israel, and to support sanctions against the Jewish state.

But for Israel partisans - including many Democrats and Republicans in Congress - BDS smacks of anti-Semitism and poses a threat to Israel.

Tlaib, 42, has Palestinian roots and represents a district of suburban Detroit, Michigan that is home to thousands of Muslims.

She argues that BDS can draw a focus on "issues like the racism and the international human rights violations by Israel right now."

Ilhan Omar accuses Israel of discrimination against Palestinians akin to apartheid but denies that she is anti-Semitic.

Her remarks in January to Yahoo News, however, sparked anger among the large pro-Israel contingent in Congress, the powerful, largely Democratic US Jewish community, and Israel itself, where BDS is seen as a national threat.

"When I see Israeli institute laws that recognise it as a Jewish state and does not recognise the other religions that are living in it, and we still hold it as a democracy in the Middle East, I almost chuckle," she told Yahoo News.

"Because I know that if we see that in another society we would criticise it - we do that to Iran, any other place that sort of upholds its religion."

The worry about the still small but growing support for BDS in the United States predates Tlaib's and Omar's political rise.

A number of states have passed or proposed constitutionally questionable legislation and policies that would penalise supporters of the boycott movement.

But the arrival of Tlaib and Omar in Congress was greeted with the first proposed federal law to fight to that end, in the Senate.