WASHINGTON, Jun. 12 (Reuters) - U.S. President Joe Biden will sign a new security agreement with Ukraine on Thursday to pledge America's long-term support to the country, during his meeting with leaders of the Group of Seven democracies in Italy, a top U.S. official said.

Biden departed for Italy on Wednesday to increase pressure on Russia over its war against Ukraine and on China for its support of Moscow and excess industrial capacity.

The agreement will make clear "our support will last long into the future... particularly in the defense and security space," White House national security adviser Jake Sullivan told reporters aboard Air Force One.

"By signing this we'll also be sending Russia a signal of our resolve. If Vladimir Putin thinks he can outlast the coalition supporting Ukraine, he's wrong," Sullivan said.

Fifteen countries have signed their own security agreements, which will strengthen Ukraine's "defensive deterrence capability," he said. The U.S. agreement will include a commitment to working with the U.S. Congress on funding Ukraine going forward but will not commit to using U.S. forces on the ground, Sullivan added.

The White House had said earlier that Biden will meet again with Ukrainian President Volodymyr Zelenskiy at the summit, followed by a joint press conference. The U.S. also expects Biden to meet India's Narendra Modi, who was sworn in as prime minister for a third term, and is waiting for India to formally confirm Modi's attendance at the summit.

The G7 leaders arrive at the summit confronting myriad woes at home even as they seek solutions for many of the world's most pressing problems.

Biden, 81, spent Tuesday evening at his home in Wilmington, Delaware, after a 12-member jury convicted his son Hunter Biden of lying about his drug use to illegally buy a gun in 2018, making him the first child of a sitting U.S. president to be convicted of a crime.

The trial followed the May 30 criminal conviction of Republican former President Donald Trump, the first former U.S. president to be found guilty of a felony. Biden and Trump are running against each other in the November presidential election and are neck-and-neck in the polls.

The heads of the world's most developed democracies will address multiple challenges during the June 13-15 meeting, including wars in Ukraine and the Middle East, trade imbalances with China, threats posed by artificial intelligence and development challenges in Africa.

The leaders will also announce new sanctions and export controls against Russia that target entities and networks helping Putin's forces fight the war in Ukraine. Efforts to curb Russia's growing war economy will be a major discussion topic, administration officials have said.

The U.S. on Wednesday dramatically broadened sanctions on Russia, including by targeting China-based companies selling semiconductors to Moscow, as part of its effort to undercut the Russian military machine waging war on Ukraine.

Separately, the Commerce Department said it was targeting shell companies in Hong Kong for diverting semiconductors to Russia, taking steps that would affect nearly $100 million of high-priority items for Moscow including such chips.

"These actions heighten the risk for financial institutions dealing with Russia's war economy, slows down avenues for evasion while diminishes Russia's ability to benefit from access to foreign technology, equipment, software and IT services," Sullivan said.

Shoring up funding for Ukraine will be a top priority at the G7 meeting, with U.S. and European officials eager to lock in solutions, ahead of a possible Trump re-election and the uncertainty it would raise over future U.S. support for Kyiv.

The Group of Seven nations and the European Union are considering how to use profits generated by Russian assets immobilized in the West to provide Ukraine with a large up-front loan to secure Kyiv's financing for 2025.

The White House's Sullivan said the U.S. is "making good progress in generating an outcome in which those proceeds from those frozen assets can be put to good use."

Biden will press other G7 leaders to agree to an innovative plan to use future interest on some $281 billion of Russian central bank funds to back up a $50 billion loan to Ukraine.

G7 leaders also face electoral challenges, with polls indicating British Prime Minister Rishi Sunak will likely lose power in a national vote next month, and the leaders of France and Germany reeling from heavy defeats in recent European elections.

Photo from Reuters