WASHINGTON (Reuters) - The U.S. State Department is withholding messages from the ambassador to the European Union that are relevant to the impeachment inquiry, the chairman of the U.S. House Intelligence Committee said on Tuesday.

“Not only is the Congress being deprived of his testimony ... but we are also aware that the ambassador has text messages or emails on a personal device, which had been provided to the State Department, although we have requested those from the ambassador, and the State Department is withholding those messages as well,” Adam Schiff told reporters.

“Those messages are also deeply relevant to this investigation and the impeachment inquiry,” Schiff added.

Representatives for the State Department could not be immediately reached for a response.

The Trump administration on Tuesday blocked the ambassador, Gordon Sondland, who had agreed to appear voluntarily, from testifying behind closed doors before three House panels, including Schiff’s.

“The failure to produce this witness, the failure to produce these documents -- we consider yet additional strong evidence of obstruction of the constitutional functions of Congress - a co-equal branch of government,” Schiff said.

“By preventing us from hearing from this witness and obtaining these documents, the president and secretary of state are taking actions that prevent us from getting the facts needed to protect the nation’s security.”