U.S. Secretary of State Mike Pompeo struck a defiant tone Tuesday when he told lawmakers he would not allow State Department staffers to heed depositions requested to take place starting this week.

Axar.az reports citing Anadolu Agency.

Pompeo was subpoenaed last week by the House Intelligence, Foreign Affairs and Oversight committees, who also requested depositions from five State Department officials beginning Oct. 2.

The top diplomat said he will comply with the committees' request to hand over Ukraine-related documents by the Oct. 4 deadline, but vowed to block former and current State Department officials from testifying about matters related to Ukraine as the House continues its impeachment investigation into U.S. President Donald Trump.

Pompeo said the efforts "can be understood only as an attempt to intimidate, bully and treat improperly the distinguished professionals of the Department of State."

"I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals whom I am proud to lead and serve alongside at the Department of State," Pompeo wrote in a letter to Eliot Engel, the chairman of the House Foreign Affairs Committee.

The depositions were scheduled to begin Wednesday with Washington's former Ukraine envoy, Marie Yovanovitch, and run through next week. The former U.S. special envoy for Ukraine, Kurt Volker, resigned from the volunteer post last Friday.

The House also sought to depose Deputy Assistant Secretary for European and Eurasian Affairs George Kent, counselor Ulrich Brechbuhl and the U.S.'s EU envoy Gordon Sondland.

The House began its impeachment investigation into Trump last week. At issue is a July 25 telephone conversation the president held with Ukrainian President Volodymyr Zelensky in which Trump repeatedly pressed the Ukrainian president to investigate former Vice President Joe Biden and his son, Hunter, over unsubstantiated claims of corruption.