Swedish activist Greta Thunberg and Portuguese left-wing politician Mariana Mortagua were among hundreds of people from 44 countries due to depart from several ports to Gaza as part of the Global Sumud Flotilla.

Sumud means “perseverance” in Arabic.

READ MORE: Israel declares Gaza City a ‘combat zone’ and suspends aid ceasefires

Israel has scuppered numerous attempts over the 15 years of the blockade, including a 2010 boarding by its special forces in which at least nine Turkish activists were killed.

The ball was in politicians’ court to put pressure on Israel to let the flotilla through, said Saif Abukeshek, one of the organisers.

“They need to act to defend human rights and to guarantee a safe passage for this flotilla,” the Palestinian, who is resident in Spain, told Reuters on Thursday in Barcelona.

In June, Israeli naval forces boarded and seized a British-flagged yacht carrying Thunberg, among others. Israel dismissed the aid ship as a propaganda stunt in support of Hamas.

It has imposed a naval blockade on the coastal enclave since Hamas took control of Gaza in 2007, saying it aims to stop weapons from reaching the militant group.

In early March, Israel also sealed off Gaza by land, letting in no supplies for three months, arguing that Hamas was diverting aid while a global hunger monitor says part of Gaza is suffering from famine.