"The (former) president of Tunisia and the Spanish lawmaker flew this morning. There are another 14 who have begun the expulsion process," a spokeswoman for Israel's immigration authority told AFP.
Israel had yesterday commandeered the Swedish-flagged Marianne of Gothenburg, part of the so-called Freedom Flotilla III, and accompanied it to the port of Ashdod.
Sixteen foreign nationals were on board along with two Israelis, Arab lawmaker Basel Ghattas and a television reporter. The two Israelis have been released, though Ghattas could face a parliamentary hearing on whether he should face sanctions.
The three other boats had turned back before the Marianne was boarded by the Israeli navy in an operation that took place without the deadly force that marred a raid to stop a similar bid in 2010.
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The activists' campaign came as Israel faced heavy international pressure over its actions in Gaza, with a UN report last week saying both the Jewish state and Palestinian militants may have committed war crimes during a 50-day conflict in the besieged coastal enclave last summer.
The reconstruction of thousands of homes destroyed during the fighting between Israel and Hamas, Gaza's Islamist de facto rulers, is yet to begin, and both Israel's blockade and a lack of support from international donors have been blamed.
In 2010, 10 Turkish activists aboard the Mavi Marmara were killed in an Israeli raid on a six-ship flotilla.