Attorney General William Barr on Wednesday cancelled plans to testify before the House of Representatives about his handling of Special Counsel Robert Mueller’s Russia investigation, further inflaming tensions between US President Donald Trump and Democrats in Congress.

Barr was due to face the Democratic-controlled House Judiciary Committee on Thursday, but pulled out after the two sides were unable to agree on the format for the hearing.Justice Department spokeswoman Kerri Kupec said Nadler’s proposal to have committee lawyers question Barr was “unprecedented and unnecessary,” saying questions should come from lawmakers.

The Justice Department also said on Wednesday it would not comply with a Nadler-issued subpoena seeking an unredacted version of Mueller’s report and underlying investigative files from the probe.Earlier on Wednesday, Barr spent more than four hours before the Republican-controlled Senate Judiciary Committee where he fended off Democratic criticism of his decision to clear Trump of criminal obstruction of justice and faulted Special Counsel Robert Mueller for not reaching a conclusion of his own on the issue.

In his first congressional testimony since releasing a redacted version of Mueller’s report on April 18, Barr also dismissed Mueller’s complaints that he initially disclosed the special counsel’s conclusions on March 24 in an incomplete way that caused public confusion.

Illustrating tensions between the two men, Barr described as “a bit snitty” a March 27 letter from Mueller in which the special counsel urged him to release broader summaries of his findings – a step Barr rejected. Trump seized on Barr’s March 24 letter to declare that he had been fully exonerated.

Democrats have accused Barr of trying to protect the Republican president, who is seeking re-election next year. They pressed Barr on why he decided two days after receiving the 448-page document from Mueller in March to conclude that Trump had not unlawfully sought to obstruct the 22-month investigation.