(CNN) A top aide to Elizabeth Warren on Wednesday accused the campaign of rival Pete Buttigieg of exploiting a loophole in campaign finance rules to influence the spending decisions of a pro-Buttigieg super PAC.

The accusation, leveled on Twitter by Warren campaign manager Roger Lau , comes just days after the Iowa caucuses, where a disappointing showing has left the Massachusetts senator racing to conserve money ahead of New Hampshire's Democratic primary next week.

Iowa officials still are counting following problems with an app used to report results. But as of late Wednesday afternoon, Buttigieg topped the field with 26.7% of state delegate equivalents, followed closely by Vermont Sen. Bernie Sanders at 25.4%.

Warren was in third place at 18.3%.

Wednesday's debate erupted after Michael Halle, a senior adviser to the Buttigieg campaign, wrote on Twitter that "Pete's military experience and closing message from Iowa work everywhere especially in Nevada where it's critical they see this on the air through the caucus."

"Was this meant to be a DM (direct message) or did you mean to tweet out this instruction to your super PAC?" Lau responded.

In a statement, Buttigieg spokesman Chris Meagher said, "Pete is the only candidate who isn't a millionaire or billionaire."

"If the largest progressive veterans group wants to help spread the word about his service we welcome it," he said, in a reference to VoteVets PAC, the super PAC spending on Buttigieg's behalf. "Veterans have been central to propelling our movement and they will be a central part of the coalition that Pete will bring together to defeat Donald Trump."

Under federal campaign finance rules, candidates -- who face strict limits on the size and source of money that can flow into their campaigns -- are barred from coordinating their advertising and spending decisions with outside groups that can raise unlimited money from wide range of sources but must operate independently of their favored candidates.

But the "coordination rules have become so porous, they are virtually meaningless," said Larry Noble, a former top lawyer with the Federal Election Commission and a CNN contributor. Halle's comments on Twitter, he added, do not "rise to the level of illegal coordination, unless you could show" he was privately communicating with the pro-Buttigieg super PAC.

VoteVets PAC has spent heavily on Buttigieg's behalf and this week reserved more than $550,000 in advertising to boost his campaign in New Hampshire ahead of Tuesday's primary there.

Buttigieg is a veteran of the Navy Reserves and served a tour in Afghanistan in 2014. VoteVets' current ad touts those credentials to argue that his military experience taught him teamwork that will serve a divided country well if he's elected president.

In a statement late Wednesday afternoon, VoteVets chairman Jon Solz denied any coordination with the Buttigieg campaign.

"We independently decide our ad strategy," he said. "We cannot and do not coordinate our ads with the campaign in any way."

The head of an outside group backing Warren, the Progressive Change Campaign Committee, quickly followed her campaign's lead and jumped into the debate on Wednesday, saying Buttigieg has "corrupted his brand by becoming the candidate of big-money corporate donors."

"It's a slap in the face of campaign finance law to so brazenly and unethically direct a Super PAC how to spend on his behalf," Adam Green, the group's co-founder, said in a statement.

Warren has relied on small-dollar donors to fuel her campaign. And her third-place showing in Iowa does not appear to have helped boost her campaign coffers for the primary slog ahead.

On Tuesday night, Warren's campaign canceled about $355,000 worth of future reservations that had been placed in Nevada and South Carolina -- the next nominating contests on the calendar after New Hampshire, according to data tracked by Kantar Media's Campaign Media Analysis Group.

Noble noted that candidates in previous election cycles have found ways to skirt the restrictions on coordination. One technique: publicly posting flattering B-roll footage of a candidate that super PACs then grab to use in their advertising.