JERUSALEM » Israel was preparing Thursday for a showdown with a flotilla of up to nine vessels carrying hundreds of pro-Palestinian activists and thousands of tons of supplies headed for Gaza, the Hamas-run coastal enclave. It was the most ambitious attempt so far to break Israel's maritime blockade of Gaza.

The flotilla of cargo ships and passenger boats, led by the Free Gaza Movement and a Turkish organization, Insani Yardim Vakfi, converged at sea from a number of countries over the last 10 days.

Israel, which says it allows basic supplies into Gaza through points along the land border, denounced the flotilla as a political provocation and has vowed not to let the boats reach Gaza. It has invited the flotilla to land at an Israeli port, Ashdod, instead.

Gaza has been under an Israeli- and Egyptian-imposed blockade since Hamas, the Islamic militant group that does not recognize Israel's right to exist, took over the territory by force in 2007. Israel, the United States and the European Union classify Hamas as a terrorist organization. The activists said the boats, which were expected to reach the coast sometime this weekend, were carrying 10,000 tons of cargo including cement, school supplies and medical equipment aimed at easing the hardship in Gaza.

Maj. Gen. Eitan Dangot, the Israeli military's chief liaison with the Palestinian-controlled territories, said Israel's policy was very clear. Briefing a group of foreign reporters in Tel Aviv this week, he said that Israel had offered the activists the chance to unload their cargo at Ashdod. Israel, he said, would be willing to transfer it, after inspection, to Gaza. But he added, “;We will not allow ships to come to Gaza while Hamas is in control there.”;

In a news statement issued by Israel's Foreign Ministry this week, Sarah Weiss Maudi, the ministry's expert on maritime and humanitarian law, said the maritime blockade was in force “;because Israel is currently in a state of armed conflict with the Hamas regime”; in Gaza. Hamas, she continued, “;has repeatedly bombed civilian targets in Israel proper with weapons that have been smuggled into Gaza by various routes, including the sea.”;

Israel was preparing to intercept the boats and divert them, if necessary, to Ashdod. Large tents and other facilities have been set up at the port to receive the activists, who number up to 800 and include public officials. An Israeli Arab lawmaker was aboard one of the boats. From Ashdod, the activists will either be voluntarily deported or detained.

The approaching flotilla has set off a public-relations war regarding the situation in Gaza.

Dangot and other Israeli officials insist that no humanitarian crisis exists. Anticipating the bad publicity that was bound to accompany the arrival of the boats, the military and the Foreign Ministry published detailed reports this week of the almost 100,000 tons of supplies that Israel says it has allowed into Gaza this year. Israel says the importing of cement and iron has been greatly restricted because Hamas uses those materials to manufacture rockets and bunkers. Nevertheless, it has allowed some building materials for about a dozen infrastructure projects supervised by international bodies. Many additional goods are smuggled into Gaza through tunnels running under the border with Egypt.

In a sarcastic e-mail to reporters this week, Israel's Government Press Office recommended a high-end restaurant in Gaza, the Roots Club, attaching the menu and a link to its website. “;We have been told the beef stroganoff and cream of spinach soup are highly recommended,”; the office said. The restaurant would, of course, be out of reach for most of Gaza's 1.5 million residents. Israeli military officials put unemployment there at almost 40 percent.

International organizations active in Gaza paint a bleaker picture. A United Nations Development Program report published on Sunday determined that about three-quarters of the damage caused by Israel's military offensive in Gaza in the winter of 2008-2009 had not yet been repaired. And a report by the United Nations humanitarian coordinator blamed the blockade for “;suffocating”; the agricultural sector in Gaza and said that insufficient food was now a problem in more than 60 percent of households.

The Free Gaza Movement has organized at least four aid voyages since the summer of 2008, usually consisting of one or two vessels. The earliest ones were allowed to reach Gaza. Others have been intercepted and forced back, and one, last June, was commandeered by the Israeli Navy and towed to Ashdod.

In other developments, police officers in Jerusalem on Thursday arrested two ultranationalist Israeli activists after they hurled insults at the White House chief of staff, Rahm Emanuel, as he toured the Old City with his family, a police spokesman said. Angry at what they view as the Obama administration's anti-Israel policies, right-wing activists had been waiting to confront Emanuel, who was in Israel on a private visit to celebrate the bar mitzvah of his 13-year-old son.

One of the arrested ultranationalists, both of them well-known provocateurs, could be heard yelling, “;Shame on you; you hate Israel”; and “;Traitor,”; according to Agence France-Presse.