An "extraordinary" security boost will accompany the final two stages of the Vuelta in the Madrid region, Spanish authorities said on Wednesday, as pro-Palestinian protests have rocked one of cycling's biggest races.

The demonstrations, which have targeted the Israel-Premier Tech team over the devastating war in Gaza, have impacted several stages of the 21-day race and cast doubt on organisers' ability to see it through to its completion.

The central government's representation in Madrid said in a statement that more than 400 extra Civil Guards will protect the penultimate stage on Saturday and 1,100 police officers will deploy for Sunday's finale.

The "extraordinary deployment" would be the police's largest security effort since Madrid hosted the 2022 NATO summit, the statement added.

"With this reinforcement, the aim is to make compatible the unfolding of the sporting event in the two Madrid stages... and the legitimate right to protest," the authorities said.

Activists have circulated calls on social media to disrupt the stages, recommending the occupation of "points of maximum visibility" in Madrid and offering advice to protesters thinking of leaping in front of the cyclists.

Race organisers had denied they were weighing whether to cancel the final stages but have suggested that Israel-Premier Tech withdraw for the other teams' safety.

Protesters have burst onto the course and caused crashes, while last week's stage 11 was neutralised before the finish in Bilbao with no winner declared due to demonstrators disrupting the run-in.

On Tuesday, hundreds of protesters blocked a road close to the finish and faced off with police, forcing stage 16 in the northwestern region of Galicia to be shortened.

Riders had said they would neutralise stage 17 on Wednesday if further protests disrupted the competition. In the end the stage finished without incident.

"In the end, racing to an undefined finish line is not really fair sport... we are just the pawns in a very large chess game," said Australia's Jack Haig of Team Bahrain Victorious.

- Widespread Palestinian support -

Israel-Premier Tech, owned by Israeli-Canadian property developer Sylvan Adams, is a private outfit and not a state team but was hailed by Israeli Prime Minister Benjamin Netanyahu for continuing to compete despite the vehement protests.

The Palestinian cause enjoys widespread support in Spain, whose poor relations with Israel nosedived even further this week after Prime Minister Pedro Sanchez announced measures aimed at stopping what he called "the genocide in Gaza".

Madrid recalled its ambassador from Tel Aviv after Israel's foreign minister accused the government of antisemitism and has barred two far-right Israeli government ministers.

Several members of Spain's left-wing coalition government have publicly supported the protests, drawing criticism from the conservative opposition Popular Party (PP) on Wednesday.

"I don't know what is more worrying, that Spain isn't capable of ensuring safety during an international sporting event, or that the government promotes that it can't be safe," PP spokeswoman Ester Munoz told reporters.

The Gaza war was triggered by an unprecedented cross-border attack on Israel by Palestinian militant group Hamas on October 7, 2023, which resulted in the deaths of 1,219 people, mostly civilians, according to an AFP tally of official Israeli figures.

Palestinian militants also seized 251 hostages on that day, with 47 still held in Gaza, including 25 believed to be dead.

Israel's retaliatory offensive has killed more than 64,000 Palestinians, mainly civilians, according to figures from Gaza's Hamas-run health ministry that the United Nations considers reliable.