U.S. President Joe Biden and Ukraine's President Volodymyr Zelenskyy are expected to sign a security deal during their meeting on the sidelines of the Group of Seven summit on Thursday, the White House said.

National Security Adviser Jake Sullivan told reporters that the agreement would not commit U.S. troops directly to Ukraine's defense against Russia's invasion - a red line drawn by Biden, who is fearful of being drawn into direct conflict between the nuclear-armed powers.

"We want to demonstrate that the U.S. supports the people of Ukraine, that we stand with them and that we'll continue to help address their security needs," Sullivan said, adding "this agreement will show our resolve."

Sullivan called the agreement a "bridge" to when Ukraine is invited to join the NATO alliance - a long-term priority of Zelenskyy's that the allies have said will first require an end to the Russia-Ukraine war.

Biden headed to Italy on Wednesday for a summit of the world's leading democracies with an urgency to get big things done.

This year's G7 summit comes three years after Biden declared at his first such gathering that America was back as a global leader following the disruptions to Western alliances that occurred when Donald Trump was president. Now, there's a chance this gathering could be the final G7 for Biden and other G7 leaders, depending on the results of elections this year.

Biden and his counterparts from Canada, Britain, France, Germany, Italy and Japan will use the summit to discuss challenges related to the spread of artificial intelligence, migration, the Russian military's resurgence and China's economic might, among other topics. Pope Francis, Ukrainian President Volodymyr Zelenskyy and President Recep Tayyip Erdoğan are joining the gathering at the Borgo Egnazia resort in the Puglia region of southern Italy.

The summit, which opens Thursday, will play out after far-right parties across the continent racked up gains of surprising scale in just-concluded European Union elections. Those victories, coupled with upcoming elections in the United Kingdom, France and the United States, have rattled the global political establishment and added weightiness to this year's summit.

"You hear this a lot when you talk to U.S. and European officials: If we can't get this done now, whether it's on China, whether it's on the assets, we may not have another chance," said Josh Lipsky, senior director of the Atlantic Council's GeoEconomics Center, an international affairs think tank. "We don't know what the world will look like three months, six months, nine months from now."

The G7 is an informal bloc of industrialized democracies that meets annually to discuss shared issues and concerns. Biden is set to arrive in Italy on Wednesday night, his second trip outside the U.S. in as many weeks. The Democratic president was in France last week for a state visit in Paris and ceremonies in Normandy marking the 80th anniversary of the D-Day landings in World War II.