(UPI) — Sen. Lindsey Graham on Thursday requested State Department documents related to former Vice President Joe Biden’s communications with former Ukrainian President Petro Poroshenko.

Graham, R-S.C., sent a letter to Secretary of State Mike Pompeo requesting the documents to assist in answering questions regarding allegations that Joe Biden was involved in the termination of Ukrainian Prosecutor General Viktor Shokin in order to end an investigation into natural gas company Burisma Holdings, where his son Hunter Biden served on the board.

The senator requested all documents and communications related to Joe Biden’s phone calls with Poroshenko on Feb. 11, 18 and 19, and March 22, 2016, citing media reports that they discussed previous demands to dismiss Shokin for alleged corruption before he was removed from office on March 29, 2016.

Graham also requested documents and communications between Joe Biden and his office and Poreshenko and his office between Feb. 2, 2016, when Burisma founder Mykola Zlochevsky’s home was raided and Shokin’s dismissal.

Lastly, Graham sought all documents and communications related to a meeting between Devon Archer, a business partner of Hunter Biden, and then-Secretary of State John Kerry on March 2, 2016.

Graham’s request comes after two weeks of public testimony on the impeachment inquiry into President Donald Trump, which centers around a whistle-blower’s complaint that Trump withheld military aid from Ukraine in an attempt to pressure newly elected Ukrainian President Volodymyr Zelensky to investigate Burisma and the Bidens.