U.S. President Joe Biden met European Commission President von der Leyen and European Council President Charles Michel on Tuesday for a summit tackling issues from trade to the COVID-19 pandemic.
The leaders also discussed climate change policy, including the EU's plan to impose carbon emissions costs on imports of goods, including steel and cement, which the Commission will propose next month.
"I explained the logic of our carbon border adjustment mechanism," von der Leyen told a news conference after the summit.
"We discussed that we will exchange on it. And that WTO might facilitate this," she said.
Brussels and Washington are keen to revitalise transatlantic cooperation on climate change, after four fractious years under former president Donald Trump.
On Tuesday, they outlined plans for a transatlantic alliance to develop green technologies and said they will coordinate diplomatic efforts to convince other big emitters to cut CO2 faster.
But the EU border levy could still cause friction. A draft of the proposal said it would apply to some U.S. goods sold into the EU, including steel, aluminium and fertilisers.
Brussels says the policy is needed to put EU firms on an equal footing with competitors in countries with weaker climate policies, and that countries with sufficiently ambitious emissions-cutting policies could be exempted from the fee.
The United States and EU are the world's second- and third- biggest emitters of CO2, respectively, after China.
A draft of the EU-U.S. summit statement, seen by Reuters, repeated commitments the leaders made at the G7 summit at the weekend to "scale up efforts" to meet an overdue spending pledge of $100 billion a year by rich countries to help poorer countries cut carbon emissions and cope with global warming.
It did not include firm promises of cash. Canada and Germany both pledged billions in new climate finance on Sunday, and campaigners had called on Brussels and Washington to do the same.
The draft statement also stopped short of setting a date for the United States and EU to stop burning coal, the most polluting fossil fuel and the single biggest of greenhouse gas emissions.
Brussels and Washington said they will largely eliminate their CO2 emissions from electricity production by the 2030s.
(Reporting by Kate Abnett, additional reporting by Valerie VolcoviciEditing by Marguerita Choy, Andrew Heavens and Barbara Lewis)
By Kate Abnett and Valerie Volcovici