In an exclusive interview with the BBC, the Ukrainian president said Russia's Vladimir Putin wanted a "long war" between the US, Israel and Iran because it would weaken Kyiv, with US resources being directed elsewhere.
Zelensky also claimed that US President Donald Trump was not on "any side" in the war between Russia and Ukraine and did not want to "irritate" Putin.
He urged Trump and Sir Keir Starmer to meet and find common ground, after the US president's repeated criticism of the UK prime minister.
Now in its third week, the conflict in the Middle East has spread across the Gulf with Iran lashing out at neighbouring states in retaliation to the US and Israel's strikes.
Zelensky said he had a "very bad feeling" about the impact of the conflict on the war in Ukraine, saying negotiations towards peace are being "constantly postponed. There is one reason - war in Iran".
He also said the situation was benefiting Putin because it increased energy prices, which was a problem for Ukraine, and meant there could be a "deficit" of missiles.
"For Putin, a long war in Iran is a plus," he said. "In addition to energy prices, it means the depletion of US reserves, and the depletion of air defence manufacturers. So we [Ukraine] have a depletion of resources."
Zelensky said there would "definitely" be a deficit of Patriot missiles which would be "a challenge", saying the question now was "when will all the stockpiles in the Middle East be exhausted".
"America produces 60-65 missiles per month. Imagine, 65 missiles per month is is about 700-800 missiles per year, produced each year," he said. "And on the first day in the Middle East war, 803 missiles were used."
Zelensky also spoke about his US counterpart's position on the Ukraine war, saying that Trump wanted to be a negotiator rather than take any side in Ukraine's war against Russia's illegal invasion.
The Ukrainian president said he thought Trump "wants to finish this war" but added that the US president and his advisers had chosen a strategy of close dialogue with Putin, and "not to irritate him because Europe irritated him and Putin does not want to talk to Europe".
