US President Joe Biden and Ukrainian leader Volodymyr Zelenskyy signed a 10-year security agreement on Thursday that they hailed as a milestone in relations between their countries, but that alone was not enough to stop Zelenskyy from wondering how much longer he could count on America's support.

Zelenskyy also said his country “urgently” needed additional air defence systems to protect Ukrainians and the nation's infrastructure from Russia's continued bombardment.

The leaders signed the agreement on the sidelines of the annual Group of Seven summit, and Biden said the goal "is to strengthen Ukraine's defence and deterrence capabilities.”

Zelenskyy said at a joint news conference that the signing made for a “truly historic day,” but he also wondered about the durability of support from the United States and other allies.

Ukraine's president said the right question to ask is “for how long the unity in the world will remain?" and how it will be influenced by the outcome of elections this year in many of those countries.

During the first day of their meeting in southern Italy, G7 nations agreed on a deal to provide US$50 billion of loans for Ukraine backed by interest from frozen Russian assets.

Although many details still need to be worked out, G7 members and the European Union are expected to contribute to the loan, with cash to reach Kyiv by the end of the year.

"This is a very historic step we're taking today," said German Chancellor Olaf Scholz. "It is also a clear signal to the Russian President (Vladimir Putin), that he can't just sit this out and hope that fiscal problems in a country that backs Ukraine will one day let him win this war."

G7 leaders are also expected to discuss China and immigration in their summit.

Pope Francis is also putting in a historic appearance at the G7 meeting, discussing artificial intelligence and holding multiple bilateral meetings including with Biden, Zelenskyy and Turkish President Tayyip Erdogan.

"It is a historic day. We will welcome the Holy Father. It is the first time for a pontiff at a G7. I am proud it will happen under the Italian presidency," Italian Prime Minister Giorgia Meloni told reporters on Thursday.

Protests were staged near the summit venue.

Demonstrators voiced support for Palestinians and accused the G7 of failing to do more in environmental protection. (AP/Reuters)