The annual Country Reports on Terrorism for 2017 said Iran and the proxy groups it finances were responsible for attacks or attempted attacks in the Middle East, Europe, South America and Africa.
"It brings to its terrorist activities the resources of a state," Nathan Sales, the coordinator for counterterrorism, said in a call with reporters.
"Iran uses terrorism as a tool of its statecraft," he added. "It has no reservations about using that tool on any continent."
The Iranian mission to the United Nations issued a statement denying it supports terrorists and accused the United States of destabilizing the region.
"Iran has fought ISIS, al-Qaida, their various associate and affiliated terror groups and other terrorist groups in our region for decades," the statement said. "The U.S., meanwhile, has destabilized the region at every turn by invading countries under false pretenses, supporting brutal invasions and occupations by its proxy states, and by supporting terrorists across the region."
Since President Donald Trump withdrew from the 2015 nuclear deal in May, the administration has taken an increasingly tough stance on Iran. In November, it will reimpose oil sanctions, which were suspended under the deal in exchange for curbs on Iran's nuclear program.
In anticipation of the sanctions, U.S. officials have been pressuring other countries to halt or drastically reduce their purchases of Iranian oil, the chief source of foreign revenue. They have threatened to impose secondary sanctions on businesses and countries that keep buying oil from Iran.
After abandoning the nuclear deal, the administration seeks to negotiate a treaty with Iran that will cover both its ballistic missile and nuclear programs, said Brian Hook, the special envoy for Iran.
In a speech at the Hudson Institute on Wednesday morning, Hook said the goal is to reach a "new deal" with Iran that ends in a treaty.
Hook acknowledged that Iranian leaders have shown no interest in talks with U.S. officials, although both Trump and Secretary of State Mike Pompeo have said they would be willing to meet with Iranians.
Iranian President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif are expected to be in New York next week for the annual meeting of the U.N. General Assembly. The Iranians are not scheduled to meet with U.S. officials.
Iran has been designated as a state sponsor of terrorism since 1984. It is one of four countries on the list, along with North Korea, Syria and Sudan.
As evidence that Iran intended to potentially launch an attack in the United States, the report cited the arrest last summer of two men in Michigan and New York suspected of being undercover operatives for Hezbollah. Iran provides financial support to the Lebanese militant group.
Overall, terrorism declined last year, Sales said. The total number of attacks dropped 23 percent, and fatalities decreased by 27 percent. Though many countries saw a decline in violence, Sales said, the decrease was primarily due to fewer deaths and attacks in Iraq.
Almost 6 in 10 attacks occurred in Afghanistan, India, Iraq, Pakistan and the Philippines. And 7 in 10 deaths were in Afghanistan, Iraq, Nigeria, Somalia and Syria.
Though the Islamic State has lost most of the territory it held in Syria and Iraq, the report said the terrorist group continued to encourage sympathizers to strike against soft targets and in public spaces. It said al-Qaida remains a formidable threat and last year expanded its membership and operations.
"Al-Qaida is a determined and patient adversary," Sales said. "They have largely remained out of the headlines in recent years. They were content to let ISIS bear the brunt of the international response. But we shouldn't confuse a period of relative quiet with al-Qaida's abandonment of its capabilities and its intentions to strike the United States and its allies."
The report said fighting terrorism has grown more complex, as groups such as the Islamic State and al-Qaida have adapted to counterterrorism pressure.
"They have become more dispersed and clandestine, turning to the Internet to inspire attacks by distant followers, and, as a result, have made themselves less susceptible to conventional military action," it said. "Further, the return or relocation of foreign terrorist fighters from the battlefield has contributed to a growing cadre of experienced, sophisticated, and connected terrorist networks, which can plan and execute terrorist attacks."
Also Wednesday, Trump renewed an emergency proclamation first issued after the 2001 terrorist attacks, extending what was supposed to be a temporary state of national emergency for another year, the White House said in a statement.
The extension of Proclamation 7463 gives the president powers to mobilize the military.
Trump published a notice in the Federal Register extending the emergency, explaining that terrorism continues to pose a threat to the national security, foreign policy and economy of the United States.