"The national emergency declared on November 14, 1979, and the measures adopted on that date to deal with that emergency, must continue in effect beyond November 14, 2019," Trump said in a letter sent to Congress on Tuesday.
The emergency declaration was first promulgated by then-President Jimmy Carter on November 14, 1979, by Executive Order 12170, Trump wrote in the letter.
"Our relations with Iran have not yet normalized, and the process of implementing the agreements with Iran, dated January 19, 1981, is ongoing. For this reason... I am continuing for one year the national emergency with respect to Iran," Trump said.
The national emergency with respect to Iran was declared pursuant to the International Emergency Economic Powers Act and took related steps to deal with the threat to US national security, foreign policy and economy constituted by the situation in Iran, he wrote.
A state of emergency gives a US president extraordinary powers, including the ability to seize property, summon the National Guard and hire and fire military officers at will.
The state of emergency also forms the basis for most US sanctions against other countries.