Thousands mobilised in Italy Thursday in support of the Gaza aid flotilla ahead of a strike in solidarity with activists, as the government repeated its criticism of the flotilla's attempt to reach Gaza.

Besides Rome, where police said 10,000 people joined a march, other protests took place in cities such as Milan, Torino, Florence and Bologna, among others.

Protesters in Rome gathered at the Colosseum and marched through the capital in solidarity with the flotilla and against Prime Minister Giorgia Meloni's support of Israel -- a day after a previous protest Wednesday evening.

"The flotilla has somehow reopened attention on this issue, revealing consciences that have perhaps been too dormant after two years of war and massacres," Rome city council member Lorenzo Giardinetti, who had joined the protest, told AFP.

"Today it is the Colosseum, tomorrow it is the general strike... It's a matter of putting our bodies on the line, as the flotilla activists did."

Another protester, 76-year-old Gianfranco Pagliarulo, said many in the crowd were there to show their opposition to Italy's government.

"Instead of defending the victims, the government defends the aggressors, and this is absolutely intolerable," Pagliarulo said.

In Milan, an estimated five thousand protesters marched towards the Duomo, blocking traffic during rush hour, according to local news agency AGI.

"We are ready to block everything. The genocide machine must stop now," shouted protesters.

Trains were suspended in Florence and Bologna due to protesters on the lines, TreniItalia said.

A general strike has been called by Italian trade unions for Friday.

Earlier Thursday, Italy said Israel had detained 40 Italians from the flotilla, as Meloni at a European Union meeting in Denmark again criticised their efforts.

"Obviously we will do everything we can to ensure these people can return to Italy as soon as possible," Meloni told reporters.

But, she added: "I continue to believe that all this brings no benefit to the Palestinian people".

Block everything

After first saying Thursday morning that 22 Italians were reportedly detained by Israel, Foreign Minister Antonio Tajani later updated that number to 40.

Tajani told parliament that all flotilla members -- from all countries -- would be transferred in a group Monday or Tuesday to the Ben Gurion airport in Tel Aviv, where two charter flights would take them to two different capital cities in Europe.

"They have asked Madrid and London," he said, without specifying who had made the request, "but they have not yet received a response."

Tajani noted that "up to this point, no acts of violence or complications have been recorded in the operation carried out by the Israeli forces".

Two Italian members of parliament and two Italian members of the European Parliament were aboard the Global Sumud Flotilla, which aims to break Israel's siege of Gaza.

On Wednesday, the Israeli navy began intercepting vessels in the flotilla after warning the activists against entering waters it says fall under its blockade.

In a statement, the flotilla organisers branded the interceptions as "illegal" since they were traversing international waters.

Ahead of Friday's general strike, the USB union said it was "time to block everything."

"Israel is violating international law," it said.

Meloni, the head of a hard-right government, had previously called the flotilla a "dangerous, irresponsible" initiative, even while Italy sent a navy frigate to provide assistance.

On Tuesday, the premier urged the flotilla to stop to avoid jeopardising US President Donald Trump's plan to end the Israel-Hamas war.