BARI, Italy (Reuters) - Group of Seven (G7) leaders start their annual summit on Thursday looking to double down on support for Ukraine in its war with Russia and offer a united face in confronting China's political and economic ambitions.

With the Middle East, migration and artificial intelligence (AI) also on a packed agenda, the June 13-15 summit in southern Italy would be taxing for leaders at the best of times, but most of them are also bowed down by their own domestic woes.

U.S. President Joe Biden, facing a tough re-election bid in November, arrived in Italy the day after his son Hunter Biden was convicted of lying about his drug use to illegally buy a gun.

British Prime Minister Rishi Sunak appears destined to lose power in a July 4 election, the leaders of France and Germany are reeling from political defeats, and opinion polls are bleak for the prime ministers of Canada and Japan.

Only the host, Italian Prime Minister Giorgia Meloni, is riding high after triumphing in Italy's European election last weekend, but achieving meaningful results in the luxury Borgo Egnazia hotel resort will be a tall order.

Determined to claim the initiative, the G7 leaders look likely to announce they have agreed on plans to issue $50 billion of loans for Ukraine using interest from frozen Russian assets to back the multi-year debt package.

However officials acknowledge the plan is complex, meaning any deal will only be in principle, with legal experts still having to thrash out the details that will need the backing of European nations, particularly Belgium, which is not in the G7.

For a second year running, Ukrainian President Volodymyr Zelenskiy will attend the summit and is due to sign a new, long-term security accord with Biden.

"By signing this we'll also be sending Russia a signal of our resolve. If (Russian President) Vladimir Putin thinks he can outlast the coalition supporting Ukraine, he's wrong," White House national security adviser Jake Sullivan told reporters.

CONFRONTING CHINA

Underscoring U.S. determination to punish Moscow for its 2022 invasion of Ukraine, Washington on Wednesday dramatically broadened sanctions on Moscow, including by targeting China-based companies selling semiconductors to Moscow.

By announcing new restrictions on Chinese firms on the eve of the G7 meeting, Biden is no doubt hoping to persuade Western allies to show greater resolve in confronting Beijing over its support for Russia and its industrial over-capacity.

The European Commission told automakers on Wednesday it would impose extra duties of up to 38.1% on imported Chinese electric cars from July, less than a month after Washington quadrupled duties for Chinese EVs to 100%.

While G7 leaders are expected to express concern over high Chinese production levels, which they say disrupt global supply chains and market stability, EU diplomats warn that Europe is anxious to avoid a full-blown trade war with Beijing.

Eager not to appear like an elitist fortress, the G7 has thrown open its doors to a large number of outsiders this year, including Pope Francis, who is expected to give a keynote speech on Friday on both the risks and potential of AI.

Among those who have also been invited to Puglia are the leaders of some of the biggest regional powers across the globe such as India, Brazil, Argentina, Turkey, Algeria and Kenya.

Although the summit is scheduled to run until Saturday, many G7 chiefs will leave on Friday night, including Biden, meaning the final day has been earmarked for bilateral meetings for those staying on and a final news conference from Meloni.

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(Reporting by Crispian Balmer, Angelo Amante, Andrew Gray, Andrea Shalal and John Irish; Writing by Crispian Balmer and Keith Weir)

By Crispian Balmer and Angelo Amante