In their first meeting, the European Union's foreign policy chief Federica Mogherini and U.S. Secretary of State Rex Tillerson spoke "at length" about terrorism, Russia, the Iran nuclear deal and Ukraine, the EU said in a statement.

Mogherini is in Washington on Thursday and Friday, for the first time since Donald Trump became president. She also met on Thursday with Michael Flynn, Trump's national security advisor, a White House official said.

Mogherini said in a statement after the meeting that she was "pleased to meet" Tillerson, and that they had an "open exchange on many dossiers that we are dealing with."

The two discussed "trans-Atlantic relations, the common challenge of countering terrorism, the ongoing work to strengthen European defense, relations with Russia, the Iran nuclear deal and the main crises, from Ukraine to Syria," the statement said.

The State Department did not provide details of what the two top diplomats for the United States and Europe discussed.

Mogherini helped negotiate the 2015 nuclear deal with Iran, along with diplomats from Iran, the United States and other major world powers. The deal curbed Iran's nuclear program in return for sanctions relief.

Trump has said the deal is terrible, and Flynn put Iran "on notice" last week for test-firing a ballistic missile, raising the prospect of spiking tensions between Iran and the United States.

Trump has expressed openness to working more closely with Russia, a stance that has rattled European allies and drawn criticism from Democrats and Republicans who say Russia is an adversary of the United States and other Western democracies.

Tillerson had significant business ties with prominent Russians in his former position as Exxon Mobil Corp's chief executive, but also referred to Russia as a "bad actor" during his confirmation hearing last month.