The package is part of US efforts to meet "Ukraine's pressing requirements by committing critical near-term capabilities while also building the enduring capacity of Ukraine's armed forces," the Defense Department said in a statement.

The assistance will not immediately arrive on the battlefield, as it falls under the Ukraine Security Assistance Initiative (USAI), under which Washington procures equipment from the defense industry or partners, rather than drawing it from US stocks.

The package includes four NASAMs air defense systems and related munitions, TOW anti-tank missiles, 152 mm artillery shells, drones as well as counter-drone systems, and various vehicles.

The announcement comes as Ukrainian forces are fighting to advance against invading Russian troops in a slow-moving counteroffensive that Mykhailo Podolyak, a senior aide to Ukraine's president, said Wednesday "will be quite difficult, long and will take quite a lot of time."

Podolyak also said that Kyiv's forces need two to three hundred tanks as well as 60 to 80 F-16 warplanes.

The Netherlands and Denmark are leading a plan to train Ukrainian pilots on using the US-made aircraft as part of an 11-nation coalition, but the effort is still in its early stages.

The pace of Ukraine's advance in the counteroffensive has raised questions about whether it will be successful, but US officials have highlighted the tough obstacles Kyiv's forces must overcome when asked about the pace of advance.

Ukrainian troops are facing heavily fortified Russian positions that include complex minefields, tank obstacles, barbed wire and trenches, Chairman of the Joint Chiefs of Staff General Mark Milley told journalists on Tuesday.

He also said that Ukraine has "a significant amount of combat power not yet committed."

"Right now, they are preserving their combat power, and they are slowly and deliberately and steadily working their way through all these minefields, and it's a tough fight."

The United States has spearheaded the push for international support for Ukraine, quickly forging an international coalition to back Kyiv after Russia invaded and coordinating aid from dozens of countries.

Washington has committed to providing tens of billions of dollars in military aid to Kyiv since Russia invaded in February 2022.