Gordon Sondland -- whose appearance before Congress is being watched especially closely as he was a Trump ally -- said he believed the president was pressing Ukraine to investigate his potential 2020 rival Joe Biden.

"We followed the president's orders," Sondland said in his prepared testimony to an open hearing of the House Intelligence Committee.

He said that Trump forced US diplomats to work with his personal lawyer, former New York mayor Rudy Giuliani.

"We did not want to work with Mr. Giuliani. Simply put, we played the hand we were dealt," he said.

Sondland said that Trump held off on offering a summit with Ukraine's new president, Volodymyr Zelensky, as Giuliani demanded that Kiev publicly announce that it was investigating a gas company on which former vice president Biden's son Hunter held a paid board position.