The leaders of two of the world's largest energy companies said June 26 they worry a trade conflict between the U.S. and other nations could destabilize the global economy.

U.S. President Donald Trump has in recent months imposed tariffs on steel, aluminum and other imports, steps that have resulted in retaliatory measures against U.S. crops, motorcycles and other products, including petroleum.

That has sparked concern amongst Chevron Corp. (NYSE: CVX), Exxon Mobil Corp. (NYSE: XOM) and other major oil and natural gas producers that Trump's actions could imperil relations with some of their largest customers, including China and the European Union.

The U.S., the world's largest natural gas producer, has begun exporting more of the fuel, part of Trump's approach to energy diplomacy. But the tariffs could undermine that plan.

"The risk of trade wars starts to weigh on people's perception of economic growth in the future," Chevron CEO Mike Wirth said at the World Gas Conference in Washington. "These things run the risk of becoming a bit of drag on growth."

Chevron tries to buy steel for its pipelines and other equipment from U.S. manufacturers but cannot always do so, Wirth said.

Darren Woods, Exxon Mobil's CEO, said his company is trying to keep a "level-headed voice" around the tariffs.

"The world has been very well served with low tariffs and free trade," Woods said. "With tariffs, you run the risk of making some projects less attractive."

Both companies are major natural gas producers in the U.S., with Chevron focused especially on the Marcellus Shale in Pennsylvania and Exxon Mobil on the Eagle Ford Shale in Texas.

The two executives, who appeared jointly on a conference panel, argued that natural gas is the best way to help cut global greenhouse gas emissions and also increase the availability of power across the developing world.

Natural gas had for several years enjoyed a designation as a "bridge fuel" away from hydrocarbons toward renewable energies. This view has come under assault recently by environmentalists, something both CEOs pushed back on.

"Renewables are terrific, but you need the lights and the power and the air conditioning all the time," said Wirth, who became Chevron's CEO earlier this year. "You've got to have a mix."

Natural gas, Woods said, "as the fuel of the future is a part of the solution to climate change."