The Israeli military attacked a Gaza-bound aid flotilla, leaving at least nine dead, after receiving reports that the fleet had links to al Qaeda, the Israeli ambassador to Denmark said Monday.

"Before the flotilla entered Israeli waters, rumor had it that the organizers [of the aid initiative] had links with the al Qaeda terrorist network," Arthur Avnon was quoted as saying on the website of public broadcaster DR.

"The people on board were not so innocent ... and I cannot imagine that another country would react any differently," the ambassador said before being summoned to the Danish foreign ministry to explain the attack.

Meanwhile, Israeli Prime Minister Benjamin Netanyahu’s office said he spoke Monday to top diplomatic and security officials by telephone from Canada and voiced his “full backing” for the military.

Before the ships set sail from waters off the east Mediterranean island of Cyprus on Sunday, Israel had urged the flotilla not to try to breach the blockade and offered to transfer the cargo to Gaza from an Israeli port, following a security inspection.

Commandos stormed the six ships carrying hundreds of pro-Palestinian activists on an aid mission to the blockaded Gaza Strip. At least nine people were killed and dozens wounded after Israeli soldiers encountered an unexpected resistance when they boarded the vessels.

According to Netanyahu, the Israeli soldiers were attacked and defending themselves in the raid.

SLIDESHOW: World Responds to Israeli Gaza Flotilla Attack

Avnon echoed Netanyahu’s sentiments, lamenting the loss of life but saying, "the [Israeli] soldiers were welcomed with violence when they climbed on board. One of them was injured in the stomach and others were injured with baseball bats."

An Israeli military spokesman said two guns had been discovered on the ships and Israel's military chief, General Gaby Ashkenazi, blamed the violence on Turkish nongovernmental organization (NGO) IHH, which he characterized as "extremist."

Israel's Channel 10 television and Al-Jazeera both reported 19 dead, but the Israeli channel later revised that number down to nine. The Gaza branch of IHH put the death toll at 15, saying most of them were Turkish nationals.

The Israeli military said seven soldiers were wounded, one of them seriously.

The operation in international waters off the Gaza coast was a nightmare scenario for Israel that looked certain to further damage its international standing, strain already tense relations with Turkey -- the unofficial sponsor of the mission -- and draw unwanted attention to Gaza's plight.

White House spokesman Bill Burton, speaking on the eve of a meeting that President Barack Obama had scheduled at the White House with Netanyahu, said the United States "deeply regrets the loss of life and injuries sustained" in the incident. Netanyahu announced Monday he would cancel his White House visit to deal with the crisis.

Burton also said that administration officials are "currently working to understand the circumstances surrounding this tragedy." The United States, among others, has been trying to restart direct peace talks between the Israelis and Palestinians, but progress toward this achievement has lagged severely in recent months.

The tough Israeli response also drew condemnations from Turkey, France and the U.N.'s Mideast envoy, while Greece suspended a military exercise with Israel and postponed a visit by Israel's air force chief.

The U.N. Security Council announced they would meet Monday afternoon to discuss the attack.

Turkey's prime minister Recep Tayyip Erdogan described the raid as "state terrorism" Monday, as some10,000 Turks marched from Israel's Consulate in Istanbul toward the city's main square, shouting slogans denouncing Israel. The protesters earlier Monday tried to storm the Consulate building but were blocked by police.

In response, Israel advised its citizens Monday to avoid travel to Turkey and instructed those already there to keep a low profile and avoid crowded downtown areas.

There were conflicting accounts of what happened early Monday.

An Al-Jazeera reporter on one of the Turkish ships said the Israelis fired at the vessel before boarding it. The Israelis, who had declared they would not let the ships reach Gaza, said they only opened fire after being attacked by activists with sticks, knives and live fire from weapons seized from the Israeli commandos.

Israeli security forces were on alert across the country. Palestinian President Mahmoud Abbas condemned the Israeli "aggression," declared three days of mourning across the West Bank and called on the U.N. Security Council and Arab League to hold emergency sessions on the incident.

Ismail Haniyeh, leader of the rival Hamas government in Gaza, condemned the "brutal" Israeli attack and called on U.N. Secretary-General Ban Ki-moon to intervene.

The activists were heading to Gaza on a mission meant to draw attention to a three-year-old Israeli blockade of the coastal territory. Israel imposed the blockade after Hamas, which it considers a terrorist group, violently seized the territory. Critics say the blockade has unfairly hurt Gaza's 1.5 million people.

"It's disgusting that they have come on board and attacked civilians. We are civilians," said Greta Berlin, a spokeswoman for the Free Gaza movement, which organized the flotilla. She spoke from the Mediterranean island of Cyprus and said she had lost contact with the flotilla.

Israeli naval commandos stormed the ships in a predawn raid while they were in international waters after ordering them to stop about 80 miles from Gaza's coast, according to activists.

A Turkish website showed video of pandemonium on board one of the ships, with activists in orange life jackets running around as some tried to help an activist apparently unconscious on the deck. The site also showed video of an Israeli helicopter flying overhead and Israeli warships nearby.

Turkey's NTV showed activists beating one Israeli soldier with sticks as he rappelled from a helicopter onto one of the boats.

The Al-Jazeera satellite channel reported by telephone from the Turkish ship leading the flotilla that Israeli navy forces fired at the ship and boarded it, wounding the captain.

"These savages are killing people here, please help," a Turkish television reporter said.

The broadcast ended with a voice shouting in Hebrew, "Everybody shut up!"

The Free Gaza Movement is an international group of pro-Palestinian activists that claims the blockade, imposed three years ago after the militant Islamic Hamas group overran Gaza, is unjust and a violation of international law.

Organizers included people affiliated with the International Solidarity Movement, a pro-Palestinian group that often sends international activists into battle zones, and the IHH, a Turkish aid group that Israel accuses of having terrorist links.

The flotilla of three cargo ships and three passenger ships carrying 10,000 tons of aid and 700 activists was carrying items that Israel bars from reaching Gaza, like cement and other building materials.

This is the ninth time that the Free Gaza movement has tried to ship in humanitarian aid to Gaza since August 2008.

Israel has allowed ships through five times, but has blocked them from entering Gaza waters since a three-week military offensive against Gaza's Hamas rulers in January 2009.

The latest flotilla was the largest to date.

NewsCore and The Associated Press contributed to this report.