Swedish author Henning Mankell was onboard one of the ships in the Gaza aid flotilla which Israeli commandos attacked early Monday, reportedly leaving 19 people dead, the Swedish branch of Ship to Gaza said.

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The 62-year-old author of the Wallander detective series joined the flotilla from Cyprus by way of smaller boats "after almost 48 hours of playing hide-and-seek with Cypriot police," Ship to Gaza Sweden said in a statement.

Mankell, whose books about world-weary detective Kurt Wallander have sold more than 25 million copies worldwide and have been adapted to film and television, said he was partaking in the flotilla to show his solidarity towards the Palestinian people.

"I think that when one talks about solidarity, one must always know that actions are what proves destiny," he told Swedish public radio last Thursday.

"It is with actions that we prove we are ready to support something we believe is important," he said.

Controversial Swedish-Israeli artist Dror Feiler, the chairman of the Swedish "Jews for Israeli-Palestinian peace," as well as nine other Swedes, including a member of parliament, were also participating in the flotilla.

It remained unclear whether any of them had been wounded in the attack.

Israel's Channel 10 TV said 19 passengers were killed and 36 wounded when Israeli commandos stormed ships carrying Palestinian activists and aid to the besieged Gaza Strip on Monday.

The ships, carrying more than 700 passengers, were on the last leg of a high profile mission to deliver some 10,000 tonnes of supplies to Gaza as part of a protest against the blockade.

Israel had said the attempt to break the Gaza blockade was illegal and warned that it would intercept the ships and detain the activists before deporting them.