Secretary of State Antony Blinken said Monday the U.S. government will return its diplomats to Ukraine starting this week with a new ambassador set to be nominated for the post, while assessing that Russia has "failed" in its war against the East European country.

He made the remarks in Poland after visiting Kyiv with Defense Secretary Lloyd Austin a day before, the first such trip by high-level officials in the administration of U.S. President Joe Biden since Russia began its invasion of Ukraine in late February.

Touching on a meeting with Ukrainian President Volodymyr Zelenskyy in the capital city, Blinken said an increased U.S. diplomatic presence in the war-battered country will be part of the process to reopen the U.S. embassy in Kyiv, which suspended its operations amid the onset of war.

"This action will strengthen the (State) Department's ongoing commitment to facilitate humanitarian relief efforts and the delivery of assistance to the government of Ukraine, while providing enhanced support to U.S. citizens," Blinken told reporters.

Biden has decided to nominate Bridget Brink, currently U.S. ambassador to Slovakia, to serve as envoy to Ukraine, Blinken also said, touting her deep experience in the region. Her nomination requires Senate approval.

On the situation of the war, Blinken said the massive security assistance and other support the United States and countries around the world are providing to Ukraine as well as the pressure Moscow is facing through sanctions are having "real results."

"In terms of Russia's war aims, Russia has already failed and Ukraine has already succeeded," the top U.S. diplomat said, noting that the principal aim of Russian President Vladimir Putin to take away Ukraine's sovereignty and independence "has not happened and clearly will not happen."

Austin, who spoke to reporters together with Blinken, said the U.S. goal is to see Ukraine remain a sovereign country and "see Russia weakened to the degree that it can't do the kinds of things that it has done in invading Ukraine."

During talks with Zelenskyy, the United States vowed to provide new assistance worth $713 million for Ukraine and other countries in the region, according to the State Department.

Since Russia launched the invasion on Feb. 24, the United States has committed roughly $3.7 billion in security assistance to Ukraine, it said.

Russian forces have retreated from around Kyiv, which they failed to seize, and have shifted their focus to the eastern and southern parts of Ukraine. The eastern Donbas region is an area where Ukrainian forces have been fighting pro-Russian separatists for years following Russia's 2014 annexation of Crimea in the south of Ukraine.