House Intelligence Committee Chairman Adam Schiff says the failure of a State Department official to show up at a deposition Tuesday as part of House Democrats’ impeachment investigation is “yet additional strong evidence” of obstruction of Congress.

The Trump administration barred Gordon Sondland, the U.S. European Union ambassador, from closed-door testimony as several committees are investigating President Donald Trump’s dealings with the president of Ukraine.

Text messages released last week revealed conversations between Sondland and other U.S. diplomats who were intermediaries as Trump urged Ukraine to investigate political rival Joe Biden’s family and the 2016 election.

Schiff and other Democrats have said that they will consider such obstruction if they draft articles of impeachment against the president.

WATCH: Republicans defend State Department barring U.S. envoy from testifying