The Biden administration backed its decision to provide advanced multiple-launch rocket systems to Ukraine on Wednesday, dismissing allegations that the decision is too late to make a difference and dismissing the Kremlin's complaint that the U.S. is extending the war.

The weapon systems, which were used by the U.S. military to target militants during the wars in Iraq, Afghanistan, and Syria, will enable Ukrainian forces to unleash several rockets at Russian artillery and infantry with speed and accuracy.

According to Colin Kahl, the undersecretary of defense for policy, the shipment of four M142 High Mobility Artillery Rocket Systems, also known as HIMARS, to Ukraine is imminent, and it will take approximately three more weeks to train Ukrainian forces on their usage. 

The armaments are part of a new $700 million package of weaponry and equipment already provided to Ukraine by the United States. According to the Pentagon, these include counter-artillery radars, Javelin anti-armor missiles, 155-millimeter howitzer artillery rounds, and Mi-17 helicopters.

"The Ukrainian defenses are not buckling. They are clinging to life, but it is a grueling battle," Kahl said, adding they expect that these additional capabilities will be available in a timely manner.

The satellite-guided, truck-launched weaponry will be the most modern arms delivered to Ukraine by the Biden administration since Russia's invasion on February 24. 

They had been requested for around two months without permission, causing dissatisfaction in both Kyiv and Washington.

Last week, Ukrainian Foreign Minister Dmytro Kuleba stated that his country required rocket systems and that some nations were "dragging their feet" in supplying Kyiv with heavy weapons.

The shipment of rocket systems was authorized after Ukraine informed the Biden administration that they would not be used for cross-border operations against Russia, Kahl said. 

The administration also decided to deliver ammunition with a range of approximately 45 miles rather than the Advanced Tactical Missile System (ATACMS) with a range of up to 186 miles, restricting Ukraine's ability to utilize the weapons.

The United States has a "good amount of capacity" to send additional HIMARS, Kahl said, but U.S. authorities wish to evaluate their use prior to further shipments.

"We need information on their usefulness and how they are being handled on the battlefield," he said.

Since Biden assumed office, the United States has provided Ukraine with $5,3 billion in security aid, the majority of which - $4.6 billion - following the invasion.