TEHRAN, Iran (AP) — Iran's president has announced that the government will begin fully implementing the landmark nuclear deal reached with world powers.

President Hassan Rouhani says in a letter published on his website Thursday that work will be done according to considerations and requirements set out by Iran's supreme leader Ayatollah Ali Khamenei.

Khamenei on Wednesday endorsed the deal but warned the government to be vigilant, saying the United States cannot be trusted.

Rouhani's letter says Iran's government will start full implementation "with good will." But it adds that Iran will be vigilant in making sure other parties fulfill their obligations.

The agreement reached in July with the U.S., Britain, France, China, Russia and Germany curbs Iran's nuclear activities in exchange for lifting crippling international sanctions.