A veteran American diplomat who was quietly paid by Boeing while pushing for the Iran nuclear deal—which paved the way for the aerospace giant to ink a $25 billion sale with Iran—is rejecting accusations that he hid a financial motive while pushing for the accord.

Thomas Pickering, a former top Clinton administration official who was on Boeing's payroll for over a decade, wrote op-eds pushing for the nuclear agreement, testified before Congress about its advantages, and discussed the deal with lawmakers — often without disclosing his connection to the aerospace giant. After the deal was implemented in January, Boeing publicly revealed its plans to sell dozens of planes to Iran Air, an airline that the Obama administration had previously sanctioned for ferrying weapons on behalf of Iran's military, including to Iranian proxies in Syria.

Pickering told THE WEEKLY STANDARD Monday that he did not know the Iran deal would benefit Boeing when he advocated for it before Congress in June 2014.

"I didn't feel there was a conflict of interest because there was no development of an interest that anybody could foresee," Pickering said. "I had no idea … until the agreement was announced in January of 2015 that there would be any portion of that allocated to airplane sales."

As nuclear negotiations came to a close last July, a Boeing spokesperson said the company would "await further developments" on how a final deal would open up Iran. An interim agreement in place from 2014 had already allowed Boeing to sell to Iran for the first time in decades.

Pickering told TWS he did not feel the need to disclose a possible financial motive for promoting the nuclear deal.

"I belong to 50 groups, advisory groups, and not-for-profit organizations. Anybody who wants to see them can read my biography," he said. "But the fact that I have to put them in a non-disclosure agreement every time I give a speech is, in my view, excessive."

The former ambassador is facing renewed criticism for not disclosing his ties as Congress readies to further debate whether to allow aircraft sales to the Islamic Republic.

"It is a great privilege to testify before the United States Congress. Those who do so have an opportunity to share their expertise and educate lawmakers on important issues facing the country," Illinois congressman Peter Roskam, whose legislation blocking the sale passed the House in July, told TWS. "If someone testifying before Congress has a financial interest in the matter at hand, that absolutely must be disclosed up front. It's not 'excessive' to let us know if you stand to make money from the policy course you're encouraging us to pursue."

A source who works closely with Congress on the Iran deal told TWS that it was broadly known the nuclear deal would enable sales like the one between Boeing and Iran.

"This doesn't pass the laugh test. Everyone knew Iran was obsessed with upgrading its airline fleet and was building it into the deal. The Iranians even used it in PR efforts, signaling they were willing to purchase Western airplanes if only their nuclear terms were met," the source said.

"Pickering was as closely involved as anyone in following the deal. Now he's saying that he didn't know what everyone else knew."

The former ambassador told TWS that Boeing did not "specifically" ask him "to work on Iran" and did not pay him to push the deal to Congress.

"I had a relationship with Boeing in which I worked on projects assigned by Boeing, and I got paid for those projects," Pickering said. "I never received a penny for anything I did on Iran on the Hill from Boeing."