JERUSALEM – The European Union on Monday called Israel’s closure of Gaza “unacceptable” and offered to play a role in opening the borders, as Israel appointed three Israeli experts and two foreign observers to a commission to investigate its deadly raid on a Gaza-bound flotilla.

The EU move added to the intense pressure Israel has faced to lift the blockade since nine pro-Palestinian activists died in clashes after Israeli commandos rappelled aboard one of the aid ships last month. The three-year closure has withheld all but the most basic supplies from Gaza’s 1.5 million Palestinian residents.

The most notable dissent has come from President Obama, who called the Gaza closure unsustainable.

The U.S. pressure resonates more with the Israelis because of their close alliance with Washington.

International envoy Tony Blair also weighed in with a call to ease the blockade and said there were indications Israel was prepared to consider doing that.

Israel has maintained the blockade to keep weapons and missiles out of the hands of Hamas, to undermine support for the Islamic militants among Gazans and to press for release of an Israeli soldier held in Gaza for four years. None of those goals has been achieved, but Israel warns that lifting the embargo altogether would allow Hamas, which does not recognize Israel’s right to exist, to bring in unlimited weapons and missiles to be turned against the Jewish state.

The 27-nation EU has consistently opposed the blockade since it was imposed in 2007, objecting to the hardships caused to the people of Gaza.

In Luxembourg on Monday, the EU described the blockade as “unacceptable and politically counterproductive,” saying in a statement it was prepared to return to an active role in helping supervise Gaza’s border crossings.

The EU helped run the Egypt-Gaza crossing before Hamas overran the territory in 2007 and the EU observers were withdrawn.

The EU, like the U.S. and Israel, considers Hamas a terrorist group and does not have direct contacts with Gaza’s rulers.

The statement said the EU would continue contacts with Israel, the Palestinian Authority of President Mahmoud Abbas — whose forces were expelled from Gaza by Hamas — and “other appropriate parties,” without mentioning Hamas.

Despite that, Hamas has felt vindicated by the outcry over the bloody flotilla attack, basking in the afterglow of this week’s first visit since Hamas overran Gaza by the top Arab diplomat, Amr Moussa of the Arab League.

Several ideas are being floated to improve the dire situation in Gaza, where people have adequate basic food but little else — no exports, few consumer products, no raw materials and few construction supplies to rebuild damage from the Israel-Hamas war 18 months ago.

The main thrust of the EU statement was a demand to open the borders to civilian goods, with strict safeguards. “To this end, full and regular access via land crossings, and possibly by sea, on the basis of a list of prohibited goods, should be the prime aim,” the statement said.

Up to now Israel has maintained a list of items it permits into Gaza through its crossings, banning the rest.

Replacing that with a list of forbidden items, like weapons, and letting everything else in is among the ideas on the table, said an Israeli official who spoke on condition of anonymity because no decision has been made.