(CNN) One of Washington's most powerful lobbying firms did not disclose the wide extent of its lucrative political work for a Ukrainian group tied to both onetime Trump adviser Paul Manafort and to pro-Russian politicians, new records show.

The firm, the Podesta Group, said nothing in a 2012 lobbying report to Congress about at least 32 meetings , emails and other communications it had with the State Department, at a time when Secretary of State Hillary Clinton was scrutinizing Ukraine's upcoming election, records show.

The new disclosures shed light on the web of contacts between Russian-leaning Ukrainians, Washington lobbyists and U.S. policymakers during the Obama administration. The Podesta Group filed new, detailed lobbying disclosures in April to augment lobbying reports from 2012 to 2014 that had given little detail.

The firm is run by Tony Podesta, whose brother, John, is a longtime adviser to Clinton and was chairman of her 2016 presidential campaign. John Podesta was a senior counselor to President Barack Obama in 2014 and had previously been lobbying partners with his brother. He is not currently affiliated with his brother's firm.

The Podesta Group was representing a Ukrainian nonprofit, the European Centre for a Modern Ukraine, as it sought to counter the Obama administration's critical stance toward Ukraine's pro-Russia government and Congress' growing annoyance with Ukraine's leaders.

In addition to its undisclosed contacts with the State Department, the Podesta Group did not disclose some contacts it had between 2012 and 2014 with Vice President Joe Biden's office, the National Security Council and Congressional offices, the records show.

The Podesta Group said some of those contacts were not "lobbying" efforts but public relations, which firms are not required to report to Congress.

"These would not constitute lobbying if there was no advocacy component," Podesta spokesman David Marin said.

By contrast, in 2013 the Podesta Group disclosed on reports that it lobbied the State Department and the NSC.

Marin declined to explain why the firm disclosed some contacts but not others. "We are simply not in a position," he said, "to comment on the reasoning behind decisions that were made over four years ago."

Several legal experts challenged the Podesta Group's interpretation, saying in interviews that any meeting with State Department officials monitoring a foreign election constitutes lobbying that must be reported to Congress under federal law.

Joseph Sandler, a Washington attorney who advises Democratic and Republican lobbyists, said it's a narrow distinction between public-relations work and lobbying, and that giving the State Department information about a foreign election would constitute lobbying.

"For what other purpose would they be providing this information if not to ultimately influence a policy or position of the U.S. government in this election?" Sandler said.

Seven meetings at a crucial time

The European Centre for a Modern Ukraine was formed in 2012 by three senior members of the Party of Regions, a pro-Russia party led by President Viktor Yanukovych and advised by Manafort.

At the time, Ukraine's government faced rebuke by the Obama administration and Congress for jailing political opponents.

The center, based in Brussels, said its mission was to strengthen Ukraine's relations with the West.

The Podesta Group said in the 2012 lobbying disclosures that the center "provides information about Ukraine to governments, business and other interested parties." Podesta lobbyists were working on "issues pertaining to relations between Ukraine and the United States."

But those descriptions mask the scope of the center's mission, said Sergii Leschenko, a Ukrainian lawmaker who investigated its origins.

"It was created to launder the reputation of Yanukovych in Europe and the United States," Leschenko told CNN. The Belgium headquarters was a ruse "to pretend like it was an international European organization."

Officials at the center could not be reached for comment.

The Podesta Group said in the new filings that it did not know who funded the center, and provided a written statement in which the center's executive director says it is not "supervised, directed, controlled, financed or subsidized" by a foreign government or political party.

The Podesta Group's work for the center peaked in October 2012 at a crucial time in U.S.-Ukraine relations. Europe's leading election observer reported in early October 2012 that candidates in Ukraine were being attacked, opposition leaders were imprisoned, and that reports were circulating of intimidation, bribery and vote-buying.

Clinton, then secretary of state, voiced concerns about the election four days before it was held and called it "an important bellwether" of the Ukrainian government's commitment to democratic institutions.

The Podesta Group went to work.

In the two weeks before and after Ukraine's election, the firm had near-daily contact with the State Department, holding seven meetings, conducting "outreach" on seven days and having conversations or email exchanges on 11 days, including with top department officials. The Podesta Group also had contact with the National Security Council on seven days in that same period.

"They were pretty open about their purpose being to give a positive perspective on the upcoming election," said a former State Department employee whom the Podesta Group met.

But the firm disclosed none of that work with State and the NSC in the lobbying report it filed with Congress for the fourth quarter of 2012. The report says the firm contacted only the House and the Senate.

"Clearly they're not disclosing everything," said Craig Holman, a lobbying expert at Public Citizen. "Money was being spent to influence State Department public policy and we are oblivious to that."

It was not until April of this year that the Podesta Group retroactively filed new lobbying reports with the Justice Department that reveal far more about its work for the center.

The Podesta Group filed the new reports after deciding that its work for the center could qualify as lobbying for a foreign government or foreign political party, which must be disclosed to the Justice Department and list many activities that do not have to be disclosed in reports filed with Congress. That includes contacts with non-profit groups and journalists, as well as meetings with officials in which a lobbyist only provides information that is not intended to affect government policy.

Other lobbying can be reported to Congress and requires disclosure only of agencies lobbied and issues discussed.

A front for Ukraine's President

The center played both sides of the aisle in US politics, also hiring Manafort's consulting firm and a Republican-leaning lobbying firm, Mercury Public Affairs.

Manafort faces scrutiny from Congress as it investigates whether Trump associates conspired with Russia to tilt the 2016 election toward Trump. Trump ousted Manafort as his campaign chairman in August after reports, which Manafort denies, that he may have received $12.7 million in illicit payments from Ukraine's government.

Manafort himself had four meetings in late 2012 and early 2013 on behalf of the center, talking with a congressman and experts in international elections and Ukraine, according to a lobbying report filed last week by another Washington firm, Mercury.

Manafort declined to comment for this story.

Manafort referred the center to Mercury in 2012, said Michael McKeon a Mercury partner. "Our task was to bring Ukraine closer to the West," McKeon said.

Marin, the Podesta spokesman, said his firm's work for the center was supervised by Manafort's consulting associate Rick Gates.

The center paid Mercury $720,000 and the Podesta Group $1 million from 2012 to 2014.

Although both the Podesta Group and Mercury have said they believed the center was an independent group that was not funded or directed by Ukraine's government, lobbying reports show extensive work for Ukraine's government.

Mercury arranged 17 meetings for Ukrainian officials with lawmakers, Congressional staffers and nonprofit group in 2012 and 2013, records show.

The Podesta Group said it arranged meetings with unnamed "Ukrainian officials."

One of those meetings connected Ukraine's foreign minister Leonid Kozhara met with Senator Christopher Murphy, a Connecticut Democrat who was chairman of the Senate Foreign Relations Committee's Europe subcommittee, Murphy spokesman Chris Harris said. Kozhara was a founder of the center and a close adviser to President Yanukovych.

The Podesta Group said it was not trying to conceal the Kozhara meeting, and that it named only former heads of state for whom it arranged meetings.

As Podesta Group lobbyists met privately with officials in Washington, they left a clear impression that they were representing Ukraine's government, according to seven people who were lobbied.

"It seemed pretty clear (the center) was just a front for Yanukovych," said Dan Harsha, who was lobbied in 2013 while he was communications director for Democrats on the House Foreign Affairs Committee. "It wasn't just an independent think tank in Europe. There are not too many nonprofits with the wherewithal or the resources to hire perhaps the most prestigious Democratic lobbying group."

Kenneth Wollack, president of the National Democratic Institute, which promotes democracy internationally, recalled meeting with Tony Podesta in April 2012 as his group was focusing on the upcoming Ukrainian election. "That's when I found out there was a connection between the Podesta Group and the Ukraine government," Wollack said.

The Podesta Group did not dispute that its employees said they were representing the Ukrainian government's interests.

"We are obviously not in a position to speculate about the contents of any conversations that took place three to five years ago," Marin said.

Marin said the firm made a "good-faith effort at the time to file complete and accurate reports" with Congress, and disclosed in several reports filed with Congress that it had lobbied the State Department and the NSC for the center.

"It's not as if the firm had any hesitancy in listing that agency [State] or any other on its reports," Marin said.