The Iranian Red Crescent is planning to send humanitarian aid by sea to Gaza in a brazen challenge to Israel's sea blockade of the coastal enclave.

The attempt to confront Israel could escalate tensions between Israel and Iran, its greatest foe, and trigger a rerun of the bungled raid on a Turkish vessel bound for Gaza last week that left nine activists dead.

The move came as Israel bowed to international pressure to conduct an investigation into the botched flotilla operation. The Israeli Defence Minister, Ehud Barak, said yesterday that Israel would conduct an internal inquiry and examine ways of easing the blockade in Gaza, a step short of the United Nations' demand for an international probe.

Earlier, United States Vice-President Joe Biden held talks with the Egyptian President, Hosni Mubarak, amid signs that Washington's support for the blockade may be wearing thin. An unnamed Egyptian security official said Egypt would keep open "indefinitely" its border crossing with Gaza. The Egyptian crossing is open only to students, medical patients and foreign passport holders.

The Iranian Red Crescent, which is backed by the Islamic regime, said it had been inundated with requests from volunteers to join its three-ship convoy to Gaza, and so has decided to extend the deadline by another two weeks. It could set sail later this month.

Israel denounced the plans as "hardcore provocation" and "a threat made before deep thinking".

"If they actually send ships, it would mean they're looking for a confrontation," said Yigal Palmor, a Foreign Ministry spokesman. He did not indicate how Israel would respond, but officials have insisted they will not allow any ships to break the blockade.

Israel has justified its land and sea blockade on the grounds that it stops the flow of weapons to the Islamist group Hamas, which governs Gaza. Critics say that the blockade has strengthened Hamas and caused a humanitarian crisis.

It remains unclear how Iran would move aid ships into the Mediterranean. The most direct route is through the Suez Canal, but Egypt, which has supported Israel's blockade of Gaza, would be likely to stop it.

At the weekend, Iran reportedly suggested that it might send the Iranian Republican Guard to protect future convoys, a move that would be viewed by Israel as a direct challenge to its authority.

The International Federation of the Red Cross, which represents the Iranian Red Crescent abroad, said that it did not have any information on the shipments and could not comment.

Israel drew global condemnation when it launched a bloody assault last week on a Turkish ship, the Mavi Marmara, which was part of a six-ship humanitarian convoy attempting to break the Gaza blockade. Israel claimed that its soldiers came under premeditated attack from hardcore activists aboard the ship. Several passengers have alleged that the shooting began before Israeli soldiers landed on deck.

Although the mission, organised by the Free Gaza Movement, was unsuccessful, it drew international attention to the humanitarian conditions of Palestinians in Gaza, who have lived under siege since Hamas seized power in 2007.

Israeli naval commandos shot dead four Palestinian divers on Monday 100 metres off the Gaza shoreline.

Israel said the men, members of the Al-Aqsa Martyrs' Brigade, a militant group loosely aligned with Mahmoud Abbas' Fatah faction, were planning an attack.

One of the survivors said that the men were unarmed and had been taking part in swimming training.

*Aid group the Iranian Red Crescent is backed by the Islamic regime but is represented by the International Federation of the Red Cross abroad.

*It says it has been inundated with requests from volunteers to join its three-ship convoy to Gaza and could set sail later this month.

*An Israeli Foreign Ministry spokesman said if Iran sent aid ships, it would mean Tehran was looking for a confrontation.

*Iran suggested that it might send the Iranian Republican Guard to protect future convoys, according to media reports.

- Independent