The United States has stepped up pressure on Israel regarding the Gaza Strip: Three weeks ago it sent Jerusalem a diplomatic note officially protesting Gaza policy and demanding a more liberal opening of the border crossings to facilitate reconstruction.

U.S. and Israeli sources say the note was followed by a verbal communication clarifying that the Obama administration thinks Israel's linkage of the case of abducted soldier Gilad Shalit and the opening of the crossings was not constructive.

The note was delivered to Israel after a decision by senior U.S. officials including Secretary of State Hillary Clinton and special Mideast envoy George Mitchell. The latter discussed the contents of the note during his visit to Israel last week.

U.S. demands on Israel's Gaza policy were also raised Wednesday during talks between Clinton and Foreign Minister Avigdor Lieberman, who is on an official visit to Washington.

The note focused on a number of issues that have troubled the U.S. administration regarding Israeli policy toward the Gaza Strip.

The note's central message was that if Israel believes that the Palestinian Authority should be strengthened vis-a-vis Hamas, it must take the necessary steps regarding the Strip.

The first task is to allow food and medicine into the territory. A senior political source in Jerusalem said the Americans have noticed some improvement here, but there has been no consistency or transparency on the types of foods permitted in.

Another issue is the transfer of cash to banks in the Strip. U.S. officials have asked that Israel continue to allow the transfer of funds from Ramallah-based banks to Gaza banks to avoid damaging the enclave's banking and financial system.

A third issue in the note was the expansion of the system for opening the border crossings, and permission to import a variety of goods that would enable imports and exports and encourage economic growth.

The note also focused on construction materials such as cement and iron, which would be used to rebuild the damage caused by Israel's three-week Gaza offensive last winter.

The U.S. administration emphasized that in parallel with its demands of Israel, it was willing to assist in establishing an international supervisory mechanism under UN auspices to ensure that the building materials were used for civilian purposes and not Hamas' fortifications.

The diplomatic note was delivered to the Defense Ministry, the Foreign Ministry and the Prime Minister's Office.

Verbally, the Americans relayed a message on Israel's linkage of the Shalit case with a more extensive opening of the border crossings. Israel is particularly insistent that unless there is progress in the negotiations for Shalit's release and a new sign of life is received, there will be no concessions on the crossings.

The United States made clear that it is dissatisfied with this Israeli policy and wants Jerusalem to reevaluate its stance. "Until you change this, it will be impossible to progress," a source quoted the American officials as saying.

"This policy has not led to progress on the Shalit case and we do not think that it is contributing to anything," the U.S. officials were quoted as saying.