The Huthis have launched more than 20 attacks on merchant ships in the Red Sea in recent weeks, saying they are acting in solidarity with Palestinians in the face of Israel's war on Hamas.

Since the outbreak of the war on October 7, the Iran-backed rebels have organised weekly protests in Sanaa but Friday's demonstration was the "largest" so far, spokesman Mohammad Abdel Salam said.

"Millions of people" took part, he said on social media platform X.

A photographer who collaborates with AFP witnessed a flypast over the crowds by rebel helicopters and warplanes.

Aerial footage released by the Huthis' Ansarullah Media Centre showed a sea of protesters flooding the capital's Al-Sabeen Square, carrying Palestinian and Hezbollah flags.

"Allahu Akbar (God is greatest). Death to America. Death to Israel," they chanted.

The demonstrators also held up pictures of Huthi fighters killed Sunday in a US strike on rebel vessels in the Red Sea.

The US military said it had sunk three Huthi boats following attacks on a container vessel run by shipping giant Maersk. The rebels said 10 of their fighters were killed.

"We challenge you, America, to approach our coasts," Huthi supporter Abdulkarim al-Marwani told AFP as he took part in the protest.

"We will make the sea, as we made the land, a graveyard for America and Israel. We will make the sea a sinking zone and an incinerator for America and Israel," he added.

The attacks on shipping by the Huthis, who control much of Yemen's Red Sea coast, have caused major disruption to a waterway that carries about 12 percent of global trade.

Twelve nations led by the United States jointly warned the Huthis on Wednesday of unspecified consequences unless they immediately halt their attacks.

But Sanaa protester Hazaa Sarhan warned: "Even if you unite the forces of the entire world and the forces of all the European countries, they will never intimidate us".