The U.S. State Department has issued an initial response to a Democratic-controlled congressional committee's request for documents related to a congressional impeachment inquiry of President Donald Trump, Secretary of State Mike Pompeo says.
"The State Department sent a letter last night to Congress, which is our initial response to the document request. We will obviously do all the things we are required to by law," Pompeo said in a news conference in Greece on October 5. He did not elaborate on the contents of the letter.
Democratic lawmakers issued a subpoena to the White House to force the release of documents related to dealings with Ukraine as part of the inquiry.
The move on October 4 by three Democratic committee chairmen in the House of Representatives is likely to raise tensions even higher between Democrats and the U.S. administration.
Representatives Elijah Cummings of the Oversight Committee, Adam Schiff of the Intelligence Committee, and Eliot Engel of the Foreign Affairs Committee said they were forced to issue the subpoena after the White House failed to produce documents they had requested in a September 9 letter.
"We deeply regret that President Trump has put us -- and the nation -- in this position, but his actions have left us with no choice but to issue this subpoena,” the chairmen said, adding that a deadline of October 18 had been set for the requested documents.
In response, White House spokeswoman Stephanie Grisham said in a statement that "this subpoena changes nothing -- just more document requests, wasted time, and taxpayer dollars that will ultimately show the president did nothing wrong."
Trump, who has suggested that Schiff be tried for treason, called the lawmaker "a sick puppy" in a Twitter posting late on October 4.
The move came hours after congressional Democrats gave Vice President Mike Pence an October 15 deadline to turn over documents on his possible role in pressuring Ukraine over military aid as part of the impeachment inquiry of Trump.
Some experts have said that it is unlikely the White House will voluntarily comply with the subpoenas and that a long court fight could ensue.
The impeachment inquiry, which Trump has called a witch-hunt, stems from a government whistle-blower's complaint that in part details a July 25 phone call with Ukrainian counterpart Volodymyr Zelenskiy in which Trump pressed for an investigation of former Vice President Joe Biden and his son, who had business dealings in Ukraine
Leading up to the call, Trump had abruptly withheld some $400 million in military funding for Ukraine, which has been battling Russia-backed separatists since 2014.
U.S. lawmakers are looking into whether Trump sought personal political gain by pushing a foreign government to investigate one of his main political rivals under the threat of withholding badly needed military aid.
WATCH: Ukraine has been thrust into a major U.S. domestic political battle, after President Donald Trump asked his counterpart in Kyiv, Volodymyr Zelenskiy, to investigate former Vice President Joe Biden and his son.
Trump has denied putting pressure on Ukraine and said he was concerned about corruption there.
The president and his allies allege that the whistle-blower complaint is part of a secret conspiracy to remove him from office.
A Trump campaign ad declared, "It's nothing short of a coup, and it must be stopped," a narrator says.