The US secretary of state says pressure will continue to be applied to Iran over its commitments to the nuclear deal as the US Congress mulls over whether to re-apply economic sanctions on Tehran.
Rex Tillerson's statement - made in Brussels on Tuesday as part of a joint address with Frederica Mogherini, the European Union's high representative - came after President Donald Trump's October decision to "decertify" the 2015 agreement, which prevents Iran from developing nuclear weapons in return for sanctions relief.
Trump has described the landmark nuclear agreement involving Iran and world powers as "one of the worst deals I've ever seen".
"We discussed ... our joint efforts under the Joint Comprehensive Plan of Action [JCPOA] to hold Iran fully compliant with the terms of that deal and fully enforce that agreement," said Tillerson.
JCPOA - agreed to by the US, China, Russia, Germany, France, and the UK - imposes restrictions on Iran's stockpiles of uranium and the capacity to enrich it.
Iran has fully adhered to the terms of the agreement, according to the International Atomic Energy Agency (IAEA), a body that seeks to promote the peaceful use of nuclear energy in coordination with the United Nations.
However, Trump has accused Iran of failing to live up to the spirit of the accord and passed the agreement to the US Congress to toughen up US policy on Iran's nuclear programme.
Congress is due to return an amended agreement to Trump for consideration in the coming days.
Tillerson said Iran "is carrying out a number of other destabilising actions in the region", including backing the Houthi rebels in Yemen's civil war, deploying weapons and forces in Syria and continuing support for Hezbollah.
"These issues and activities of Iran cannot be ignored and cannot go unanswered, and we intend to continue to take action to ensure Iran understands this is not acceptable to us, and we look forward to working with our European partners in that regard," he said.
Mogherini, however, again expressed support for the nuclear deal, saying scrapping it would do more harm than good.
"Dismantling an agreement on nuclear issues that is working - as the International Energy Agency has certified nine times - would not put us in a better position to discuss all the rest, on the contrary," she said.
The US Department of State told Al Jazeera the Iran deal has many "serious flaws" that are being addressed.
"The president has directed his administration to work with Congress and our partners to fix the JCPOA. We are not encouraging Congress to reimpose sanctions at this time. The secretary’s comments today are entirely consistent with the approach laid out by the president," a spokesperson said.