U.S. officials are furious with the United Nations for its role in Hamas' attempt to enlist U.S. Sen John Kerry to transfer a letter from the Palestinian militant group to President Obama during Kerry's trip to the Middle East, an official source told FOX News.

The incident also has raised security concerns over how much Hamas knew about Kerry's travel plans.

Kerry turned the letter over to the U.S. consulate in Jerusalem on Friday, saying he was unaware that it was from Hamas until hearing about the letter in media reports, including on the BBC. He told FOX News on Saturday that he will not be visiting Hamas leader Khaled Meshaal during his trip to Syria on Saturday. He is scheduled to meet with Syrian President Bashar Assad.

U.S. officials in Jerusalem are outraged at the United Nations Relief and Works agency for apparently handing the letter off to Kerry.

The official source who spoke to FOX News argued that if the U.N. had a letter from Hamas, it should have given U.S. officials a heads-up before the news was leaked to media organizations.

The Hamas official who wrote the letter confirmed to FOX News that he wrote Obama personally, asking him not to be biased toward Israel in its conflict with the Palestinians and to act fairly. He also said Hamas is ready to talk directly to a new American administration. 

This Hamas official insists he had the backing of the group to write the letter, but it appears the official acted alone.

Kerry turned the letter over to the U.S. consulate in Jerusalem on Friday and his spokesman told FOX News that the Democratic senator was not aware that the letter was from Hamas when he accepted it from an official with the U.N. relief agency.

Kerry told FOX News that he never read the letter because it was sandwich among other promotional papers the U.N. gave him. A State Department official confirmed to FOX News that it was from Hamas and is now under review.

A potential concern was whether such a letter would violate the United States' policy toward Hamas. Obama has said his administration will not engage in diplomatic talks with Hamas unless the group renounces terrorism and affirms Israel's right to exist.

In addition, a U.S. official said there were security issues with the letter. The official who spoke to FOX News said there is concern that Hamas had advance notice that Kerry was visiting, which may raise issues of trust with the U.N. on future diplomatic trips.

FOX News' Reena Ninan and Nina Donaghy contributed to this report.