Israel is under heavy international pressure to attend a review by a United Nations agency scheduled for Tuesday in Geneva. On Friday, German Foreign Minister Guido Westerwelle sent a personal letter to Prime Minister Benjamin Netanyahu, warning that Israel’s failure to attend the Human Rights Council’s Universal Periodic Review would cause the country severe diplomatic damage and Israel’s allies around the world would be hard-pressed to help it.

Israel has boycotted the Geneva-based agency since March 2012. Then Foreign Minister Avigdor Lieberman severed ties with the council in wake of the agency’s decision to convene an international inquiry into Israeli settlements in the West Bank and Jerusalem.

Every few years, each UN member state undergoes a UPR, in which the Human Rights Council evaluates its performance in upholding human rights. The UPR is a fundamental component of the human-rights regime internationally.

If Israeli representatives fail to report for Tuesday's review, it will become the first state to boycott the review process, exposing it to international criticism as well as blame for creating a precedent that states such as Iran, Syria and North Korea might follow.

Westerwelle’s letter to Netanyahu was delivered to Emmanuel Nahshon, deputy chief of the Israeli embassy in Berlin, with the instruction that the prime minister receive it as soon as possible.

In the letter, the contents of which were obtained by Haaretz, Westerwelle acknowledged Israel’s difficult position in the Human Rights Council and emphasized Germany’s efforts to keep Israel from being unfairly singled out in the agency’s deliberations, but warned of the serious consequences in the event that it refuses to attend its UPR.

Westerwelle’s letter comes after weeks of negotiations between Israel and a group of friendly Western states on an agreement that would enable Israel to resume cooperation with the HCR.

Israel has announced two conditions for attending Tuesday’s review. The first is joining, as a full member, the council’s Western Europe and Others Group. Israel does not belong to any of the UN's regional groups, a situation that adds to its isolation and is an obstacle to winning support in the council for its positions.

Second, Israel seeks to limit use of the council’s Article 7, which stipulates that every conference must include a separate discussion on human rights in Israel – a requirement made of no other UN member.

In their negotiations with Israel, Western European states have agreed to remain silent during discussions convened during the next two years in accordance with Article 7 - a measure that would, in effect, make the discussions meaningless. However, in regard to Israel’s joining WEOG - which would require the unanimous approval of the group’s members - the European states gave only a promise rather than a binding commitment. Israel is demanding a firm commitment on this issue before it agrees to attend Tuesday’s review.

Spain currently holds the presidency of WEOG. On Thursday, its ambassador to the HRC announced that Israel's application to join the regional group would be at the top of its agenda when it convenes early next month.

Immediately after the announcement, a meeting was held between Eviatar Manor, Israel's ambassador to the UN in Geneva, and his counterparts from the United States, Germany, Canada, Britain and France. They made it clear to Manor that they would not go beyond issuing a positive statement until, and unless, Israel reported for its UPR on Tuesday, saying Israel must take the step of attending the review.

In his letter to Netanyahu, Westerwelle expressed a similar sentiment, writing, "Israel's participation in the review will create the best conditions for its being accepted into the Western European and Others Group."