US Ambassador Nikki Haley is urging countries at the United Nations to back a US-drafted resolution condemning the Palestinian Hamas movement, warning in a letter that the United States takes the vote "very seriously."
The UN General Assembly is scheduled to vote Thursday on the draft resolution that would condemn Hamas for firing rockets into Israel and demand that it ends the violence.
If adopted, it would mark the first time that the assembly has taken aim at Hamas, the Islamist militant group that has ruled the Gaza Strip since 2007.
In a letter sent to UN diplomatic missions, Haley warned that there could be attempts by some countries to introduce amendments to the text and urged ambassadors to vote against any such proposed changes.
"The United States takes the outcome of this vote very seriously," wrote Haley in the letter dated Monday and obtained by AFP.
"The resolution has been carefully-crafted to address a specific problem, and it reflects consultations with many stakeholders to ensure balance.
"That is why we are asking that you not only vote in favor of the resolution but that you also vote against any amendments or other efforts to undermine adoption of the text," she added.
Haley, who steps down as UN ambassador in January, has steadfastly supported Israel in its confrontation with Hamas in Gaza and chastised the United Nations for criticizing both sides.
The influential UN ambassador has not shied away from pressuring countries to support the US stance at the United Nations.
Arab countries are expected to put forward amendments to the resolution and push for a ruling at the General Assembly that would specify that the measure must be adopted by a two-thirds majority, instead of a simple majority.
The United States has won crucial backing for the measure from the European Union after it agreed to add a mention of relevant UN resolutions. The text does not however refer specifically to the two-state solution.
The European Union, like the United States, considers Hamas a terror group, but the 28-nation bloc is divided over how to support peace efforts.
The vote on Thursday follows the adoption in the assembly of about a dozen resolutions on the Israeli-Palestinian conflict that condemn Israeli settlements and call for progress toward the two-state solution.
Resolutions adopted by the General Assembly are non-binding, but they carry political weight and are seen as a barometer of world opinion.