The White House says it is not currently planning to ask Congress for new Ukraine funding before the end of the fiscal year at the end of September, pitting administration officials against some lawmakers and congressional staffers who are concerned that the funds could run out by mid-summer.

"Thanks to the bipartisan Congressional support for Ukraine, we believe we have the resources we need through the end of this fiscal year," a White House spokesperson told CNN. "As we get closer to the end of the fiscal year, we'll reevaluate and determine what additional resources are needed."

The White House statement comes amid some anxiety on Capitol Hill about what they say is the administration's lack of clarity on the issue. Administration officials told CNN that they anticipate that the White House's Office of Management and Budget will have to ask Congress for more Ukraine funding once the current batch -- approved by Congress in December -- runs out.

In December, Congress approved the administration's request for an additional $48 billion to help arm Ukraine and combat the Covid-19 pandemic, $36 billion of which was specifically allocated for Ukraine. The supplemental was meant to last through September 30, 2023. The administration requested this kind of additional funding to help support Ukraine four times last year, in March, May, September and December.

Pentagon spokesman Lt. Col. Garron Garn told CNN that of the $36 billion in emergency supplemental funding the Pentagon received to aid Ukraine for 2023, "$2.3 billion remains available for Presidential Drawdown Authority (PDA is an authority and not funding) and $4.0 billion for the Ukraine Security Assistance Initiative (USAI)."

Garn added that the Pentagon "continues to assess planned obligations for remaining FY 2023 funding and evaluate as the situation evolves to support battlefield successes during new offensives in the Spring."

White House and Pentagon officials told CNN that they are anticipating having to ask Congress for more funding, but want to first determine how to distribute the money they already have. To date, the US has dispersed weapons and supplies to Ukraine through the Ukraine Security Assistance Initiative and the Presidential Drawdown Authority, which draws directly from Pentagon weapons stocks and requires replenishment funding.

Congressional staffers told CNN that based on how much the administration has been spending every month, they believe the remaining funds could run out sooner than September -- and they have not yet heard from administration officials about whether the White House will request additional funding once that money is depleted.

"It is critical that the administration provide Ukraine with what it needs in time to defend and take back its sovereign territory," Sen. Susan Collins said during a Department of Defense budget hearing last week. "We expect the administration not to wait until the eleventh hour if the Ukrainians need more before the end of the fiscal year."

The staffers also said they are concerned that the administration is waiting to see whether Ukraine is successful in its much-anticipated counteroffensive before committing any more funds to the war.

US has promised to support war effort 'for as long as it takes'

Biden administration officials have said repeatedly that the US will support Ukraine "for as long as it takes" to secure Ukraine's freedom from Russian aggression.

"You remind us that freedom is priceless; it's worth fighting for as long as it takes," President Joe Biden told Ukrainian President Volodymyr Zelensky while in Kyiv in February. "And that's how long we're going to be with you, Mr. President: for as long as it takes."

Congressional staffers and administration officials took note when House Speaker Kevin McCarthy pledged to support continued assistance to Ukraine in recent weeks, after repeatedly saying that there should not be a blank check when it comes to continued support.

"I vote for aid for Ukraine, I support aid for Ukraine," McCarthy said while he was visiting Israel earlier this month. "We know that you don't support the current unlimited and uncontrolled supplies of weaponry and aid to Ukraine."

Still, congressional staffers told CNN they worry that a new supplemental request may also take longer to debate and approve now that the House of Representatives is controlled by Republicans, some of whom are skeptical of the US' ongoing support for Ukraine. That could further delay new funding, and risk creating a gap in US support for Kyiv.

Some State Department officials have already begun considering what they would do if Congress cuts funding to Ukraine, one official told CNN. And officials who oversee certain buckets of assistance like direct budget support to Ukraine remain concerned, especially given opposition to that kind of support from some Republicans, another US official told CNN.

But the White House, for its part, does not seem concerned that additional funding won't get passed. "We're extremely grateful and proud of the strong bipartisan support for Ukraine as the people of Ukraine defend their sovereignty and their democracy from Russian aggression," the White House spokesperson said.