Foreign ministers from the G7 group of rich nations aim to give what Germany called a "powerful sign of unity" as they meet on Friday to discuss the war in Ukraine, fears that the conflict could spill over into Moldova, and food security concerns.

The annual meeting running until Saturday brings together top diplomats from Britain, Canada, Germany, France, Italy, Japan, the United States and the European Union to a 400-year-old castle estate in the Baltic Sea resort of Weissenhaus.

"They will defy Russian attempts to split the world over Ukraine," German Foreign Minister Annalena Baerbock said ahead of the meeting. "Never since the end of the Cold War have we G7 partners been more profoundly challenged. Never before have we stood more united," she tweeted.

Topping the agenda is the war in Ukraine, following promises by G7 leaders last weekend to deepen Russia’s global isolation, including a pledge to ban or phase out buying Russian oil.

British Foreign Secretary Liz Truss said it was vital to keep pressure on Russian President Vladimir Putin by supplying more weapons to Ukraine and imposing further sanctions. The foreign ministers of Ukraine and its smaller neighbour Moldova will also attend.

Germany this weekend separately will host ministers from NATO, as Sweden and Finland gear up to apply for membership of the transatlantic alliance, drawing threats of retaliation from Moscow.

International alarm over Moldova

The war in Ukraine has sent global prices for grains, cooking oils, fuel and fertilizer soaring, with United Nations agencies warning that the price hikes will worsen a food crisis in Africa in particular. Russia's invasion has disrupted shipping in the Black Sea, a major route for grains and other commodities, throttling exports.

"There are 25 million tonnes of grain currently blocked in the Ukrainian port of Odesa, which means food for millions of people in the world that is urgently needed, above all in African countries and in the Middle East," Baerbock told reporters. "That's why we're sending a clear signal today- we see you, we hear you and we support you," she said.

France's Foreign Minister Jean-Yves Le Drian said it was crucial for the G7 to show that Moscow was the root cause of the global food insecurity. "We will continue our support efforts but I would add that we need to deal with a conflict that will last and the long-term consequences on food security. We need to show that Russia's aggression against Ukraine is provoking the global food crisis."

Diplomatic sources said the aim was for the seven countries to organise themselves better to find quick and efficient answers to the food crisis.

While US Secretary of State Antony Blinken will not make the meeting due to catching COVID-19, the remaining ministers will aim to reassure Moldova.

It is struggling to cope with the refugee flow from neighbouring Ukraine, and incidents involving pro-Russian separatists in the Transdniestria breakaway region have raised international alarm that the war could spread over the frontier. "The country has been weakened because of the war, so we need to confirm our support for Moldova," a French diplomatic source told reporters.

Indonesian Foreign Minister Retno Marsudi, whose country currently holds the presidency of the Group of 20 Industrialised and Emerging Economies (G20), which also includes Russia, will also join the meeting on Friday to discuss food security.

A French official said the question of Russia's presence at the heads of state meeting in November would be brought up.