President Volodymyr Zelensky’s chief of staff spoke by phone with Vice President Kamala Harris’s national security adviser, Ukraine said today, the first such call since she emerged as the frontrunner for the Democratic presidential nomination.

Andriy Yermak, head of Zelensky’s presidential office, and Phil Gordon discussed the situation at the front and Russia’s campaign of aerial attacks on Ukrainian cities and energy infrastructure, Yermak’s office said.

“He (Yermak) emphasized the importance of strengthening Ukrainian air defense with modern Western systems,” the statement said.

Zelensky referred to the conversation in his nightly video address, recalling that Harris had represented the United States at last month’s peace summit in Switzerland.

“It is important that the dynamics of our joint work for a just peace do not diminish,” Zelensky said. “All our partners at all levels know and will continue to know the prospects for a just peace to be restored as soon as possible.”

The United States has been a vital wartime ally of Ukraine, supplying many billions of dollars of military and financial assistance since Russia launched its full-scale invasion in February 2022.

Harris is seen as most likely to replace Joe Biden on the Democratic presidential ticket after the U.S. president dropped out of the race. Republican ex-president Donald Trump who is standing for re-election has threatened to cut aid to Ukraine if he wins.

Zelensky’s chief of staff and Gordon discussed further U.S. support and the outcome of an international summit held in Switzerland in June, Yermak’s office said.

Kyiv has repeatedly said it will work with whoever is elected in the United States later this year and that it does not want to be seen taking sides in a domestic U.S. matter.

A Ukrainian official who asked not to be named told Reuters: “Speaking of … Harris, we believe that two words best describe her potential foreign policy toward Ukraine and Europe as a whole — if she gets elected — continuity and predictability.”

But the official added: “At the same time, we are certain that supporting Ukraine is a national, not partisan interest for the United States.”