Secretary of Defense Lloyd Austin on Thursday held firm to U.S. and NATO opposition to implement a no-fly zone over Ukraine and said Russian forces are relying largely on ground-based missile systems. 

"The systems that are being used by the Russians to engage Ukrainian forces currently – they're using a lot of rockets and missiles and artillery," Austin said. "There are a number of things that can be used to counter that."

Austin said the use of drones has become "very effective," along with Ukraine’s ability to engage in counter-fire by utilizing rockets and artillery to launch munitions at Russian forces.  

U.S. Secretary of Defence Lloyd Austin

Defense Secretary Lloyd Austin speaks during a news conference at the Ministry of Defense of the Slovak Republic in Bratislava, March 17, 2022. (Reuters/Radovan Stoklasa)

RUSSIA INVADES UKRAINE: LIVE UPDATES

"I think increasingly we'll see the Ukrainian forces turn to those methods," he added. 

President Biden announced this week that it would provide Ukraine with another $1 billion in defensive aid to counter Russian troops pummeling cities and towns across the nation. 

The U.S. will send 3,000 shoulder-launched surface-to-air missiles, including 800 Stinger anti-aircraft systems and 2,000 Javelin missiles. 

Another 1,000 light anti-armor weapons, 6,000 VT-4 anti-armor systems and 100 tactical unmanned aerial systems will also be provided.

A load of 100 grenade launchers, 500 rifles, 1,000 pistols, 400 machine guns, 400 shotguns and 200 million rounds of ammunition will be included to help fight the ongoing ground war in Ukraine. 

Russia has hit several civilian targets, including a theater in Mariupol that was sheltering roughly 1,000 men, women and children in the besieged city. 

Ukrainian President Volodymyr Zelenskyy once again pleaded with the U.S. Wednesday to enforce a no-fly zone to stop the barrage of missile strikes that Ukraine has endured for more than three weeks.

But Austin said though Russian forces have been utilizing cruise missiles "fired from aerial platforms," they have been launched from inside Russian borders.

russia ukraine

A man carries his child away from the damage done by the shelling of a maternity hospital in Mariupol, Ukraine. (AP Photo/Evgeniy Maloletka)

RUSSIA ACCUSES WEST OF 'RUSSOPHOBIA,' THREATENS TO 'PUT IN PLACE' ITS ENEMIES

"So a no-fly zone would not have prevented that activity," he told reporters during a joint press conference with Slovak Defense Minister Jaroslav Nad Thursday. 

"POTUS was clear, we would not have U.S. forces fighting in Ukraine," he added. "No-fly zone means you are in combat with Russia, our president said we are not getting into a fight with Russia."

Zelenskyy has also requested NATO send MiG-29 warplanes, S-300 anti-aircraft missile systems or other "similar systems" in lieu of a no-fly zone.

Bulgaria, Greece and Slovakia reportedly have Russian-made S-300s – which are capable of taking down cruise missiles and warplanes – and Slovak officials said they will look to send their defenses to Ukraine. 

Nad on Thursday said Slovakia is working with the U.S. to see how its defense system could be replenished should it transfer its anti-aircraft systems to Kyiv. 

Ukrainian soldier Mariupol

A Ukrainian serviceman guards his position in Mariupol, Ukraine, Saturday, March 12, 2022. (AP Photo/Mstyslav Chernov)

CLICK HERE TO GET THE FOX NEWS APP

"We're willing to do so immediately when we have a proper replacement," Nad said, telling reporters that the S-300s are its "only strategic air defense system."

"So what would happen immediately when we decided to give it to Ukrainians is that we actually create a gap, a security gap, in NATO," he added. 

Austin said the U.S. is continuing to work with NATO allies to transfer arms where needed as it too looks to bolster its defenses against Russia.