The U.S. House Ethics Committee said it found no evidence of wrongdoing by a bipartisan group of 10 lawmakers who went on a 2013 trip to Azerbaijan paid for by that country's government.
Lawmakers obtained prior approval for the trip from the ethics panel and did not know that two groups that claimed to sponsor the trip had apparently lied about the true source of their funding, the ethics panel said.
"When a House member...seeks and receives advance written permission to accept a gift" such as travel, "that permission acts a shield to protect the individual from future action by this committee," the ethics panel said in a 28-page report on July 31.
The panel issued 12 subpoenas during its investigation, but was hampered by a lack of cooperation from key witnesses, including the Houston business executive who organized the trip.
The Washington Post reported in May that Azerbaijan's state-owned oil company paid $750,000 to cover the lawmakers' travel expenses, sending funds through two Houston-based nonprofits.
The ethics panel said it could not determine the truth of those claims, in part because of uncooperative witnesses.