When asked by journalists whether U.S. President Joe Biden is going to simplify the obstacles for Ukraine's entry into the alliance, he answered categorically "no," explaining that Ukraine must meet common standards, CNN reports.

"No. Because they gotta meet the same standards. So I'm not gonna make it easier," he told reporters Saturday ahead of his departure to Philadelphia for his first official presidential campaign event.

"I think they've done everything related to demonstrating the ability to coordinate militarily, but there's a whole issue of, is their system secure? Is it non-corrupt? Does it meet all the standards everyone, every other nation in NATO, does? I think it will. I think it can. But it's not automatic," he said.

CNN previously reported that Biden and his team are in the midst of a high-stakes conversation with fellow NATO members on how and when Ukraine may join – a debate that could expose strains in the alliance ahead of a key summit next month in Vilnius, Lithuania.