Henry Cueller, a Democrat, accused of accepting bribes in exchange for advancing interests of Azerbaijan in Congress.

The federal indictment unsealed in Houston on Friday accused Cuellar, 68, and his wife, Imelda, 67, of conspiracy and bribery as part of an influence peddling scheme. As part of the plan, federal prosecutors allege, Cuellar, a Democrat, delivered a pro- Azerbaijan speech on the floor of the US House.

Cuellar said in a statement that he and his wife “are innocent of these allegations”.

“Everything I have done in Congress has been to serve the people of South Texas,” Cuellar wrote.

The couple was taken into custody after surrendering to authorities, according to the Department of Justice.

The payments to the couple went through a Texas-based shell company owned by Imelda Cuellar and two of the couple’s children, according to the indictment.

That company allegedly received payments from the Azerbaijan energy company of $25,000 per month under a “sham contract”.

While the payments were purportedly for unspecified strategic consulting and advising services, the indictment said the contract was actually used to “disguise and legitimate the corrupt agreement between Henry Cuellar and the government of Azerbaijan”.

Federal investigators also said Imelda Cuellar had sent a falsified invoice to the Azerbaijan energy company’s Washington, DC, office stating her work was complete.

“In fact, Imelda Cuellar had performed little or no legitimate work under the contract,” the indictment said. Both Cuellars were charged with conspiracy and bribery.

The charges come months after US Senator Bob Menendez, also a Democrat, was indicted on allegations that he accepted bribes in exchange for political favours, including advancing the interests of officials with the Egyptian government.

Authorities said they found gold bars and large amounts of cash stuffed in envelopes in Menendez’s home, which they said were related to the corruption scheme.

At the time, Menendez was the chairman of the Senate Committee on Foreign Relation and wielded major influence over arms sales to Egypt and other US policy.

Menendez pleaded not guilty to the charges in September.