Egypt's deposed president has accused the army chief who overthrew him of treason, in a speech made on his behalf by his legal team on Wednesday. In only his second public statement since being arrested and held incommunicado this July, Mohamed Morsi also repeated the accusation that his overthrow constituted a military coup.

"This is a crime and treason," read lawyer Mohamed al-Damaty on Morsi's behalf. "A crime because it has all the manifestations of a coup, and treason because it betrayed the oath that the defence minister swore to the armed forces and to the Egyptian people when he took his position."

The statement marked an escalation in rhetoric from his outbursts on the first day of his chaotic trial last Monday. While appearing in court on charges of incitement to murder, Morsi had stopped short of laying the blame for his overthrow on General Abdel Fatah al-Sisi, the army chief and defence minister who toppled Morsi following days of mass protests calling for military intervention.

The speech appeared to be an attempt to rally his Islamist support base, with little to mollify the millions who marched for his removal in July. It also appeared to ignore the realities of Egypt's new status quo, which sees Morsi's supporters firmly on the back foot against a resurgent security state. Thousands of his followers have been arrested since July, and around 1,000 killed at various protests since his overthrow.

"This coup will fall by the strength of the Egyptian people and their fight for rights and freedom," Morsi's statement said. It added: "What has happened won't convince me to give up what I promised you before my election – to uphold the interests of the people above all else."

Morsi's lawyers said the former president would continue to reject the authority of the court. He caused chaos at his trial last week by refusing to recognise the court or let his legal team formally represent him, and by frequently speaking out of turn. After meeting him in jail in Alexandria for the first time since he was arrested, his defence team said this strategy would continue.

Morsi later claimed that Egypt – rocked by protests and an insurgency in the Sinai peninsula since his removal – would not see stability unless he was reinstated. "Egypt won't heal unless we end all the aspects of this coup and bring to justice all those who shed blood in all the corners of the nation," Damaty said on his behalf.

Morsi's statement also seemed to suggest that he had been arrested a day before Sisi officially announced his removal. Sisi told Egyptians of Morsi's overthrow in a televised speech on the evening of 3 July. But Morsi's statement on Wednesday said he was arrested on 2 July, an odd claim given that he himself made a televised speech to the nation that night. One of Morsi's senior aides also met the Guardian on the morning of 3 July near where Morsi was staying, and said that even at that late stage the president's fate was not yet sealed.

Morsi is currently on trial for inciting the murder of protesters outside Cairo's presidential palace last December. His allies say the charges are political. But lawyers for the victims say that whatever the circumstances of his arrest, the accusations are valid and were laid long before any suggestion that Morsi would be overthrown.