Answering questions from reporters upon arrival in New Orleans, Biden said he has been briefed every four to five hours for the last six to eight days on Ukraine's action.
"It's creating a real dilemma for Putin," he said in his first substantive comments about the operation, which appeared to have caught the Russians off guard.
The U.S. has provided billions of dollars of weaponry to Ukraine intended largely for defensive purposes, as Ukraine tries to repel the Russian invasion launched in February 2022.
The White House said Ukraine did not provide advance notice of its incursion, which took place in the Kursk region of Russia. Russian forces on Tuesday struck back at Ukrainian troops with missiles, drones and airstrikes.
White House spokesperson Karine Jean-Pierre, speaking to reporters aboard Air Force One, said Washington had no involvement in the operation.
“We had nothing to do with this," she said.
"We have no involvement. We’ll continue to have conversations with the Ukrainians about their approach, but it is really for them to speak to," she added.
Putin has said he believed Ukraine's operation was aimed at improving Kyiv's negotiating position ahead of possible talks and slowing the advance of Russian forces along the front.
U.S. officials say the objectives of Ukrainian President Volodymyr Zelenskiy remain to be seen.
"We’re trying to figure out exactly what they are doing and the goal here, and it’s still not 100% clear," said a U.S. official.
