JERUSALEM -- Israeli naval forces shot and killed four men wearing wet suits in the waters off the coast of Gaza Monday, and a militant group said they were members of its marine unit training for a mission.

The attack was the latest escalation in tensions over the 3-year-old blockade of Gaza. It came a week after Israel raided a Gaza-bound flotilla carrying humanitarian supplies and hundreds of activists protesting the closure of the Hamas-ruled Palestinian territory. Israeli soldiers killed nine activists in a clash on one of the flotilla boats, bringing fierce international condemnation and new pressure to ease the blockade.

Vice President Joe Biden said Monday the U.S. is closely consulting with Egypt and other allies to find new ways to "address the humanitarian, economic, security, and political aspects of the situation in Gaza." He spoke in the Egyptian Red Sea resort of Sharm El-Sheikh after meeting Egyptian President Hosni Mubarak.

The closure has been in place since 2007, when the Islamic militant Hamas seized the territory and it has kept out all but basic humanitarian goods. Israel and the West consider Hamas a terror group responsible for firing thousands of rockets at Israel and carrying out hundreds of attacks, including suicide bombings. Hamas does not recognize Israel's right to exist.

Israel hoped the blockade would weaken Hamas, prevent the entry of weapons and bring pressure for the release of an Israeli soldier captured in 2006, but those objectives have yet to be achieved.

The latest clash took place early Monday. The Israeli military said a naval force spotted the Palestinians in the waters off Gaza and opened fire. It claimed the forces had prevented an attack on Israeli targets.

The Palestinian militant group Al-Aqsa Martyrs' Brigades said the four killed were members of its marine unit who were training in Gaza's waters. Al-Aqsa, a violent offshoot of Palestinian President Mahmoud Abbas' Fatah faction, made the claim in a text message sent to reporters in Gaza. Four bodies were retrieved and taken to a hospital in central Gaza, said Moawiya Hassanain, a Palestinian health official. The Palestinian naval police said two people were still missing.

"The bloody escalation today is a desperate attempt by the occupation government to divert the world attention away from the massacre committed against the flotilla," Hamas spokesman Sami Abu Zuhri told reporters in Gaza.

The flotilla clash has brought renewed international focus on Israel's blockade of Gaza, which Egypt has also enforced along its border with the impoverished coastal strip.

The killings seriously damaged Israel's relations with Turkey, which had been its closest ally in the Muslim world. Turkey unofficially supported the flotilla and eight of the nine activists killed were Turkish citizens. One held dual Turkish-American citizenship. Turkey has said it will reduce military and trade ties with Israel and shelved discussions of energy projects. It has also threatened to break ties unless Israel apologizes.

In Istanbul, a 20-member Asian security group kicked off a summit with Turkey seeking to condemn Israel for the raid.

In a reflection of Israel's growing isolation, Vietnam asked Israeli President Shimon Peres to put off a scheduled working visit this week, given the current atmosphere. His office said he would go ahead with a planned visit to South Korea.

Israel's government has been frantically trying to counter the wave of harsh international condemnation that has left the Jewish state isolated and at odds with some of its closest allies.

Israel has sought to portray the nine activists killed as militants, saying they prepared for the fight before boarding the flotilla. The military Monday released the names of five of the activists it said have long ties to terror organizations.

The army also said that Gaza's Hamas rulers were preventing the transfer of clothing, blankets and medical equipment from the flotilla that Israel was trying to provide.

Israel has also come under heavy pressure to agree to an international investigation of the raid on the Turkish-flagged Mavi Marmara, the lead ship in the flotilla.

Prime Minister Benjamin Netanyahu has rejected a proposal by U.N. chief Ban Ki-moon for an international commission to investigate the raid, but officials said Netanyahu was open to a probe that would look into the actions of the activists as well.

Late Sunday, Netanyahu's office released a statement saying he discussed the international criticism with world leaders, including Vice President Joe Biden, the president of France and the premier of Canada.

Netanyahu told them any country would act in self defense if it were targeted by thousands of rockets as Israel has been by Gaza militants.

Videos released by the military have shown a crowd of men attacking several naval commandos as they landed on a ship from a helicopter, beating the soldiers with clubs and other objects and hurling one soldier overboard.

Also Monday, Palestinian officials said Israel fired a missile at militants near the Gaza border, wounding one. The military said it targeted a group of militants preparing to fire rockets at Israel. The military said 10 rockets and mortars have been fired from Gaza in the past three weeks.