A U.S. Army veteran who independently and voluntarily fought in Ukraine warned on Thursday that the hardest days of fighting the war are still to come, as the Russian military tightens its control over territory in the eastern part of the country.

Retired U.S. Army Staff Sgt. James Vasquez, who has returned from combat in the country but plans to go back, told the congressional Helsinki Commission during a briefing that while the Ukrainian military is better off now with increased foreign support, the most difficult fighting lay ahead for soldiers.

"We have much more support now, and we have the weapons and gear that we need to be able to fight properly," Vasquez said to the panel. "The fight's harder than it was when I left. And that was hard fighting when I left."

Vasquez shared moving and oftentimes difficult details of his time in Ukraine at the hearing, alongside retired U.S. Marine Corps Lt. Col. Rip Rawlings, who is providing logistical support to the Ukrainian military through he and Vasquez' foundation, Ripley's Heroes.

Vasquez, who has gained a social media following through the videos he shares from the battle's front lines, said he has "pretty much sold everything I owned" so he can return to the fight in Ukraine.

Vasquez explained the evolution of Ukrainian combatants that he witnessed, saying when he arrived the soldiers were fighting "primitively" but then saw them turn into battle-tested warriors.

"I was fighting with guys who had a red T-shirt on and sneakers," said Vasquez. "We were going into battle with white Toyota Camrys with Javelin (missiles) in the back."

But as the fighters have grown more sophisticated, and weapons and gear has rolled in from other countries, Vasquez and Rawlings both warned that the fighting situation was fragile and said Ukraine needs continued support from allies.

"We need more, they need more (weapons)," Rawlings said. "We are at a very tenuous and fragile point. This war could go in any direction, very unfortunately."

Rawlings also urged lawmakers to amend export controls that do not allow Americans to send certain military equipment, including certain body armor, to Ukraine.

"It is the largest single obstacle that we face," Rawlings said. "The biggest issue that we have is that a U.S. citizen can go purchase a set of level three body armor, but you cannot purchase it and give it to a Ukrainian."

Rep. Joe Wilson (R-S.C.) lauded the veterans for their decision to volunteer in the Ukrainian conflict at the briefing.

"Foreign fighters have actually come in to heroically volunteer and are enduring intense combat conditions and witnessing the gross human rights violations perpetrated by (Vladimir) Putin."