US Secretary of State Mike Pompeo said on Saturday that the State Department intends to follow the letter of the law during an investigation aimed at impeaching head of state Donald Trump, the AP reported.

Pompeo did not answer the questions raised regarding Trump’s intention to force Ukraine and China to investigate the activities of his Democratic political opponent Joe Biden.

During a conversation with reporters in Greece, Pompeo said the State Department sent a letter to Congress on Friday evening as a preliminary response to a request for documents.

“We’ll obviously do all the things that we’re required to do by law,” he said.

He also allowed Democrats to summon several witnesses for questioning next week. Among them is Gordon Sondland, the U.S. ambassador to the European Union, another key figure in the probe.

Earlier in Washington, there was a major scandal of allegations that Trump put pressure on Ukrainian President Volodymyr Zelenskyy to encourage Kyiv to help the head of the Washington administration reelect for a second term in 2020. It was assumed that the American leader pressured his Ukrainian counterpart, seeking the start of an investigation into the actions of the son of ex-US vice president Joseph Biden in exchange for providing financial and military aid of Washington to Kyiv. On Tuesday, the House of Representatives of Congress, controlled by the Democratic Party, announced on the basis of such suspicions that it had launched an impeachment proceedings against Republican Trump. Democrat Biden is now Trump's most likely rival in the upcoming US elections next year.

Later, the White House unveiled the transcript of the July conversation between the leaders of the two countries. It turned out that Trump did not get Volodymyr Zelenskyy to start an investigation against Hunter Biden in exchange for financial and military assistance from the US to Ukraine. The US Justice Department, which simultaneously serves as the Attorney General, found no violations of national law, and no grounds for further investigation or other actions in the content of the July telephone conversation between the American and Ukrainian presidents.