UNITED NATIONS — After hours of negotiations, the United Nations Security Council early on Tuesday condemned “acts” resulting in the deaths of nine civilians in Israel’s attack on an aid flotilla trying to breach the Gaza blockade.

In a formal statement that seemed less forceful than what had been demanded by the Palestinians, Arab nations and Turkey, the council also demanded an impartial investigation into the confrontation.

The statement urged that aid ships seized in the raid on Monday be released along with civilians held by Israel.

“The Security Council deeply regrets the loss of life and injuries resulting from the use of force during the Israeli military operation in international waters against the convoy sailing to Gaza,” the statement said, adding that the 15-member body “in this context, condemns those acts which resulted in the loss” of lives.

The wording seemed designed to dilute demands for condemnation exclusively of Israel, which argues that its soldiers acted in self-defense in response to violent resistance to their interception of the vessels from passengers on board. After the raid, Israel seized hundreds of activists as well as the ships.

“The Security Council requests the immediate release of the ships as well as the civilians held by Israel,” the United Nations statement said, calling for “a prompt, impartial, credible and transparent investigation conforming to international standards.”

It also said the situation in Gaza, under blockade by Israel, was “not sustainable” and called for a “sustained and regular flow of goods and people to Gaza, as well as unimpeded provision and distribution of humanitarian assistance throughout Gaza.”

On the broader Palestinian-Israeli confrontation, the Security Council renewed calls for a two-state solution and voiced concern that the raid on the flotilla took place while United States-sponsored so-called “proximity talks” were under way.

Earlier, Turkey — the unofficial sponsor of the convoy — had proposed a statement that would have condemned Israel for violating international law and demanded a United Nations investigation, the prosecution of those responsible for the raid and compensation for the victims. It also called for the end of the blockade.

But the Obama administration refused to endorse a statement that singled out Israel, and it proposed a broader condemnation of the violence that would include the assault by passengers of the Israeli commandos as they landed on the deck of the ship.

As the wrangling continued late Monday night and in the early hours Tuesday, the two countries were trying to work out their differences on the wording, including whether to specify that the investigation should be conducted by outsiders, diplomats said.

While condemnation of Israel in the Security Council is not uncommon, the criticism at the emergency session called by Turkey and Lebanon was notable for both its vehemence and for the broad array of countries demanding an independent investigation into the decision to fire on civilians in what they described as a humanitarian mission.

Foreign Minister Ahmet Davutoglu of Turkey, whose country’s once close relations with Israel have deteriorated markedly since Israel’s invasion of Gaza in 2009, called the attack “tantamount to banditry and piracy; it is murder conducted by a state.”

Noting that the ships were carrying items such as a playground equipment, cancer medicine and milk powder, he said that given the history of the Jews the Israelis should be more conscious than others of “the dangers and inhumanity of ghettoes as the one we currently witness in occupied Gaza.”

Gerard Araud, the French ambassador, said the death toll indicated “there was disproportionate use of force and a level of violence which nothing justifies and which we condemn.”

Nawaf Salam, the Lebanese ambassador, said even the laws of war require the delivery of humanitarian aid.

Several envoys said Israel was in violation of international law, not least because Security Council resolution 1860, passed in January 2009 during the Gaza war, had called for ending the blockade and opening unfettered access to humanitarian assistance throughout the strip. The diplomats also demanded immediate access to their citizens, with some 32 different nationalities among the estimated 600 to 700 people on the flotilla. Israel seized all six ships and forced them into port.

The United States, which habitually defends Israel in the council, said that the attempt to run the blockade by sea was ill advised.

“Direct delivery by sea is neither appropriate nor responsible, and certainly not effective, under the circumstances,” said Alejandro Wolff, the deputy permanent representative of the United States. But he also described the situation in Gaza as “unsustainable” and called on Israel to undertake a credible investigation.

Daniel Carmon, the deputy Israeli ambassador, scoffed at the idea that the ships were a humanitarian convoy — Israel had offered to bring the goods into Gaza over land — and said Israeli commandos acted in self-defense after being attacked with “life threatening means; live ammunition, knives, clubs, deck furniture and others types of weaponry.”

He described the organizers as linked to a variety of Islamic terrorist organizations, which the Turkish foreign minister called a lie.

The International Crisis Group, a nonprofit organization which seeks to end conflicts, issued a statement condemning the attack but noted that it was an outcome of the failed policy of many countries, not just Israel, in trying to isolate the Hamas government which controls the Gaza strip and thus turn the population against it.

Neil MacFarquhar reported from the United Nations, and Alan Cowell from London.