U.S. Ambassador to the United Nations Nikki Haley has ramped up pressure on Iran ahead of a trip to Vienna next week, where she will meet with international atomic watchdog officials concerning Tehran’s nuclear activities.

Haley on Tuesday rejected threats from Iranian President Hassan Rouhani, who warned the country could walk away from its nuclear agreement with world powers “within hours” if the United States continued to impose new sanctions.

Rouhani said recently enacted sanctions targeting Iran’s ballistic missile program violated its pact with the United States and five other world powers, which aimed to limit Tehran’s nuclear activities in exchange for the lifting of sanctions related to the program.

Haley said the sanctions were separate from the deal and were instead imposed “to hold Iran responsible for its missile launches, support for terrorism, disregard for human rights, and violations of UN Security Council resolutions.”