WASHINGTON (AP) — The House Ethics Committee said Friday it found no evidence of wrongdoing by a bipartisan group of 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 "in good faith" 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.

The panel said it issued 12 subpoenas and reviewed 190,000 pages of materials during its investigation, but was hampered by a lack of cooperation from key witnesses, including the Houston business executive who organized the trip.

Two Houston-based nonprofit corporations had reported to the ethics panel that they were sponsoring the May 2013 conference in the capital city of Baku, near the Caspian Sea.

The Washington Post reported in May that Azerbaijan's state-owned oil company allegedly paid $750,000 to cover travel expenses and gifts for the lawmakers by sending funds through the nonprofits.

The ethics panel said it could not determine the truth of those claims, in part because key witnesses refused to cooperate. Kemal Oksuz, a Houston public relations director who served as president of the Turquoise Council of Americans and Eurasians and was a key organizer of the trip, invoked his Fifth Amendment right to refuse to testify, the ethics panel said.

A total of 10 members of Congress — six Democrats and four Republicans — went on the trip, including former Rep. Steve Stockman, R-Texas, who left Congress in January.

Rep. Yvette Clarke, D-N.Y, a member of the ethics panel, was among those who went on the trip, which also included at least 32 House staffers. Clarke recused herself from the ethics panel inquiry.

Congressional rules generally bar foreign governments from paying for travel by members of Congress or otherwise trying to influence U.S. policy.

Four of the lawmakers who went on the trip are from Texas, a leading energy-producing state, while another is from Oklahoma, another energy leader. Lawmakers have said the purpose of the trip was to strengthen U.S. relations with Turkey and Azerbaijan, which is rich in oil and natural gas.

Texas Democratic Reps. Ruben Hinojosa and Sheila Jackson Lee attended the conference, as did Stockman and fellow Texas Republican Rep. Ted Poe and Oklahoma Republican Rep. Jim Bridenstine.

Also on the trip were Democratic Reps. Gregory Meeks of New York, Danny Davis of Illinois and Michelle Lujan Grisham of New Mexico, as well as Republican Rep. Leonard Lance of New Jersey.

The ethics panel said that the lawmakers who went on the trip received a variety of gifts, including scarves and rugs. Because of the murky nature of the trip's sponsorship, the lawmakers have all returned the gifts or "otherwise disposed of" them on a voluntary basis, the ethics panel said. The committee said it has contacted House staffers and provided guidance on how to handle any gifts received.

The ethics chairman, Rep. Charles Dent, R-Pa., and its senior Democrat, Rep. Linda Sanchez of California, said in a joint statement that the panel would take no further action and considers the matter closed.