The supporters of the Gaza-bound aid flotilla had more than humanitarian intentions. The Gaza Freedom March made its motives clear in a statement before Monday’s deadly confrontation: “A violent response from Israel will breathe new life into the Palestine solidarity movement, drawing attention to the blockade.”

There can be no excuse for the way that Israel completely mishandled the incident. A commando raid on the lead, Turkish-flagged ship left nine activists dead and has opened Israel to a torrent of criticism.

This is a grievous, self-inflicted wound. It has damaged Israel’s ties with Turkey, once its closest ally in the Muslim world; given the Hamas-led government in Gaza a huge propaganda boost; and complicated peace talks with the Palestinian Authority in the West Bank.

It also has made it much tougher for the Obama administration to persuade the United Nations Security Council to put new sanctions on Iran’s nuclear program — which Israeli officials insist is their top priority.

The questions raised by the confrontation — and there are many — demand an immediate and objective international investigation.

Why did Israel, which has blocked some ships but allowed others to pass, decide to take a stand now? Did it make a real effort to find a compromise with Turkey, which sanctioned the flotilla? Israel has a right to stop weapons from going into Gaza, but there has been no suggestion that the ships were carrying a large cache.

Was boarding, especially in the dark, the only means of stopping the ships? What happened once Israeli forces got on board? The Israeli Defense Forces have distributed a video showing that the commandos were attacked. Why weren’t they better prepared to defend themselves without using lethal force?

There is a bigger question that Israel — and the United States — must be asking: Is the blockade working? Is it weakening Hamas? Or just punishing Gaza’s 1.4 million residents — and diverting attention away from abuses by Hamas, including its shelling of Israeli cities and its refusal to accept Israel’s right to exist?

At this point, it should be clear that the blockade is unjust and against Israel’s long-term security.

After Hamas seized control of the Gaza Strip in 2007, Israel — with Egypt’s help — imposed a blockade on many goods and most people going into and out of the territory. The goal was to quickly turn residents against their new government. Three years later, Hamas is still in charge — and the blockade has become an excuse for any and all of the government’s failures.

The situation in Gaza is grim. Eight out of 10 people depend on international aid agencies to survive. Basic foodstuffs are available, but medical supplies and construction materials are severely lacking. The desperation could be seen on Tuesday when Egypt lifted the blockade and several thousand Gazans rushed the border but were later sent home after police officers said they did not know when the crossing would be opened.

On Tuesday, President Obama expressed his “deep regret” over the flotilla incident. He is doing Israel no favors with such a tepid response. Prime Minister Benjamin Netanyahu has shown time and again that he prefers bullying and confrontation over diplomacy. Washington needs to make clear to him just how dangerous and counterproductive that approach is.

Mr. Obama needs to state clearly that the Israeli attack was unacceptable and back an impartial international investigation. The United States should also join the other permanent members of the United Nations Security Council — Britain, France, Russia and China — in urging Israel to permanently lift the blockade.

That would lessen the suffering of the people in Gaza. And it would give the United States more credibility as it presses both Israelis and the Palestinian president, Mahmoud Abbas, to negotiate a peace deal.