WASHINGTON — The House on Thursday overwhelmingly approved $1 billion in new funding for Israel’s Iron Dome missile defense system, after a debate that exposed bitter divisions among Democrats over U.S. policy toward one of its closest allies.

The vote was 420-9 to help Israel replace missile interceptors used during heavy fighting in a devastating rocket and missile war with the Palestinians in May, reflecting the widespread bipartisan support in Congress for Jerusalem that has persisted for decades.

But the lopsided vote came only after days of acrimony between progressives who have accused Israel of human rights abuses and other lawmakers, including party leaders, who said they were appalled and astonished by their colleagues’ refusal to fund a defense system to protect Israeli civilians.

Bitter recriminations over the measure spilled onto the House floor on Thursday, as some progressive Democrats who were opposed called Israel an “apartheid state” and proponents hurled accusations of antisemitism. By the end, Rep. Alexandria Ocasio-Cortez of New York, a vocal critic of Israel who had come under scathing criticism from pro-Israel activists for refusing to back the measure, was in tears after switching her “no” vote to “present.”

The back and forth was the latest flare-up in a long-simmering feud between an energized new generation of progressive Democrats — many of them people of color — that has demanded an end to conditions-free aid to Israel and others in the party who argue that the United States must not waver in its backing for Israel’s right to defend itself.

In an angry speech, Rep. Ted Deutch, D-Fla., said he would not allow “one of my colleagues to stand on the floor of the House of Representatives and label the Jewish democratic state of Israel an apartheid state.”

“To falsely characterize the state of Israel is consistent with those who advocate for the dismantling of the one Jewish state in the world,” he said. “When there is no place on the map for one Jewish state, that’s antisemitism, and I reject that.”

Despite the angst, only eight Democrats — as well as one Republican, Rep. Thomas Massie of Kentucky — ultimately opposed the measure.