JERUSALEM - Israeli commandos rappelled down to an aid flotilla sailing to thwart a Gaza blockade yesterday, clashing with pro-Palestinian activists on the lead ship in a botched raid that left at least nine passengers dead.

Bloodied passengers sprawled on the deck and troops dived into the sea to save themselves amid hand-to-hand fighting that injured dozens of activists and six soldiers. Hundreds of activists were towed from the international waters to Israeli detention centers and hospitals.

International condemnation was swift and harsh as Israel scrambled to explain how what was meant to be a simple takeover of a civilian vessel went so badly awry.

President Obama voiced "deep regret" over the raid and the White House said he and Prime Minister Benjamin Netanyahu agreed by phone to reschedule White House talks "at the first opportunity."

In a statement issued by presidential aides in Chicago, where Obama and his family had been spending the Memorial Day weekend, the president was said to have "expressed the importance of learning all the facts and circumstances" surrounding the incident.

"He said he understood the prime minister's decision to return immediately to Israel to deal with today's events," the statement said. Netanyahu had been scheduled to meet with Obama today at the White House.

The raid brought heightened attention to Israel's blockade of the Gaza Strip, imposed after the Palestinian militant group Hamas seized control of the tiny Mediterranean territory in 2007. The blockade - along with Israel's offensive against Gaza in the winter of 2008-2009 to stop Hamas rocket fire - has fueled anti-Israeli sentiment around the Muslim world.

Key regional ally Turkey withdrew its ambassador yesterday, the U.N. Security Council held an emergency session, the British foreign secretary demanded an end to the blockade of Gaza, and Jordan called Israel's raid a "heinous crime."

Most of the information about what happened on the single ship where violence broke out came from Israel, which cut off all communication to and from the activists and provided testimony and video evidence that its soldiers came under attack by activists armed with metal rods, knives, slingshots and two pistols snatched from the troops.

Passengers reached at an Israeli hospital and journalists aboard the ship accused the soldiers of using excessive force. One passenger, who identified himself as American, spoke briefly with reporters.

"I'm not violent. What I can tell you is that there are bruises all over my body. They won't let me show them to you," he said before he was pushed away by a security escort.

A soldier identified only as a sergeant told reporters at a military briefing that the activists on board "were armed with knives, scissors, pepper spray and guns." He said he was armed only with a paintball rifle. "It was a civilian paintball gun that any 12-year-old can play with," he said. "I saw my friends on the deck spitting blood."