WASHINGTON, July 12 (Reuters) - Democratic and Republican senators renewed an effort to block any U.S. president from leaving NATO on Wednesday, as leaders of the alliance attended an eventful summit in Vilnius, Lithuania.

The joint resolution, seen by Reuters, is a fresh effort by Congress to prevent the president from withdrawing from the alliance without the Senate’s approval.

“The President shall not suspend, terminate, denounce, or withdraw the United States from the North Atlantic Treaty, done at Washington, DC, April 4, 1949, except by and with the advice and consent of the Senate, provided that two-thirds of the Senators present concur or pursuant to an Act of Congress,” the measure says.

Lead sponsors include Democratic Senator Tim Kaine, a member of the Foreign Relations and Armed Services committees, and Republican Senator Marco Rubio, vice chairman of the intelligence committee, who is also a senior member of the foreign relations panel.

The bill has been introduced repeatedly in recent years, including during the term of former Republican President Donald Trump, who voiced a desire for the United States to leave the military alliance.

It has yet to pass the full Senate, but an aide to Kaine noted that it was backed by the foreign relations committee last year with strong bipartisan support and that, given the war in Ukraine and the expansion of NATO, backers expect stronger support than ever.

The current president, Democrat Joe Biden, has been a strong supporter of NATO, backing its expansion and working with other members, especially on the response to Russia’s invasion of Ukraine. He is expected to celebrate its unity over Ukraine in a speech at the Vilnius summit on Wednesday.

The summit included an inaugural session of the NATO-Ukraine Council, a body established to upgrade relations between Kyiv and the 31-member transatlantic military alliance.