Among the passengers on the commandeered ship were Tunisia’s former president Moncef Marzouki and Arab-Israeli lawmaker Basel Ghattas.
A flotilla of four boats carrying pro-Palestinian activists had been seeking to reach the Gaza Strip to highlight the Israeli blockade of the territory that they called “inhumane and illegal”.
Three boats were said to have turned back while the fourth, the Marianne of Gothenburg, was boarded by the Israeli navy.
An AFP photographer said the Marianne, accompanied by a number of Israeli vessels, arrived at the port city of Ashdod and docked after nightfall, at around 1830 GMT.
The Israeli military had closed off the dock to the media.
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.
After the overnight operation to intercept the flotilla, Prime Minister Benjamin Netanyahu lauded the navy’s actions and insisted his government was right to take action against Hamas.
“In accordance with international law, the Israeli navy advised the vessel several times to change course,” the military said in a statement.
“Following their refusal, the navy visited and searched the vessel in international waters in order to prevent their intended breach of the maritime blockade of the Gaza Strip.
“The forces have reported that use of force was unnecessary, and that the process was uneventful,” it added.
A military spokeswoman confirmed to AFP that the vessel was the Swedish-flagged Marianne of Gothenburg, part of the so-called Freedom Flotilla III.
Organisers of the flotilla said the vessel was a fishing trawler carrying medical equipment and solar panels with 18 people from nine countries on board.
— Freedom Flotilla (@GazaFFlotilla) June 29, 2015
– ‘Crime of the blockade’ –
The Freedom Flotilla Coalition questioned Israel’s version of the operation and said on its website that it had “no reason to believe that Marianne’s capture was ‘uneventful'”.
Hamas, in a statement as well as in comments on Twitter, condemned the “kidnapping” of the activists, adding that “this ship succeeded in showing the crime of the blockade”.
The other three ships had changed course and were “heading back to their ports of origin”, according to a statement by “Canadian Boat to Gaza” issued by the activists before the Israeli navy commandeered the Marianne.
Netanyahu dismissed the organisers’ goals.
“This flotilla is nothing but a demonstration of hypocrisy and lies that is only assisting the Hamas terrorist organisation and ignores all of the horrors in our region,” he said in a statement.
Netanyahu said the blockade was necessary to stop weapons from arriving in the Gaza Strip by sea and that the operation “was done in accordance with international law”.
A spokeswoman for Israel’s immigration authority told AFP the foreign activists would be granted a hearing before being deported, as was the case with Gaza-bound boats intercepted in 2012.
Ghattas was expected to face a hearing in a parliamentary committee on whether he should face sanctions.
Israel imposed its blockade on Gaza in 2006 after Hamas captured an Israeli soldier, and tightened it a year later when Hamas consolidated its rule.
Israel controls the waters around Gaza and residents are not allowed to travel more than six nautical miles from the coast.
Land crossings are also strictly controlled by Israel, apart from the Rafah checkpoint with Egypt.
A number of flotillas had reached Gaza prior to May 2010, when 10 Turkish activists aboard the Mavi Marmara were killed in an Israeli raid on a six-ship flotilla.
Since then, several ships manned by pro-Palestinian activists have tried to reach the shores of Gaza, but they have all been repelled by the Israeli navy.
Critics of the blockade have called for it to be fully lifted to allow reconstruction, warning that without it an ongoing humanitarian crisis could fuel further conflict.
Some “1.8 million Palestinians (are) living in disgraceful, prison-like conditions as a result of Israel’s military siege of both sea and land,” lawmaker Ghattas said in a letter to Netanyahu before the flotilla set sail- AFP