President Joe Biden and Japanese Prime Minister Fumio Kishida began their first formal talks on Friday as they face fresh concerns about North Korea's nuclear program and China's growing military assertiveness.

The virtual meeting comes after North Korea earlier this week suggested it might resume nuclear and long-range missile testing that has been paused for more than three years.

North Korea's Kim Jong Un on Thursday presided over a Politburo meeting of the ruling Workers' Party at which officials set policy goals for 'immediately bolstering' military capabilities to counter what were described as the Americans' 'hostile moves,' according to the Korean Central News Agency.

Both the U.S. and Japan also are concerned about China's increasing aggression toward Taiwan. China claims self-governing Taiwan as its own territory, to be annexed by force if necessary. In recent months, it has stepped up military exercises near the island, frequently sending warplanes near Taiwan's airspace.

Japan remains concerned about China intentions in the South China Sea, where it has stepped up its military presence in recent years, and the East China Sea, where there is a long-running dispute about a group of uninhabited islets administered by Tokyo but claimed by Beijing.

White House officials said the two leaders were also expected to discuss ongoing efforts in the COVID-19 pandemic and the brewing crisis in eastern Europe, where Russia has massed some 100,000 troops near its border with Ukraine. Biden earlier this week said he believed Russian President Vladimir Putin is likely to order a further invasion of Ukrainian territory but he did not think Putin wanted an all-out war.

Japanese officials said Kishida, who is from Hiroshima, on which the U.S. dropped an atomic bomb at the end of the World War II, is eager to discuss a 'world without nuclear weapons' during the summit.

Biden and top aides have sought to rally the support of NATO partners and other allies to respond with harsh sanctions against Russia if it moves forward with military action.

On Thursday, in preparation for the leaders' call, Biden's national security adviser Jake Sullivan and his Japanese counterpart, Takeo Akiba, held their own call to discuss North Korea, China and 'the importance of solidarity in signaling to Moscow the strong, united response that would result from any attack' on Ukraine, according to the White House.

Secretary of State Antony Blinken and Defense Secretary Lloyd Austin also held virtual talks earlier this month with Japanese Foreign Minister Yoshimasa Hayashi and Defense Minister Nobuo Kishi, where China's military maneuvering and North Korea's nuclear program were discussed.

Friday's virtual meeting is the first substantial exchange between the leaders since Kishida took office in October. The leaders had a brief conversation on the sidelines of a climate summit in Glasgow in November. Biden was the first leader to call Kishida, on the morning of his first full day in office.

Biden, who has sought to put greater focus on the Indo-Pacific amid China's rise as a world power, had built a warm relationship with Japan's last prime minister, Yoshihide Suga, and is hoping to build a similar rapport with Kishida.