Convicted Boston bomber Dzhokhar Tsarnaev will speak at a court hearing Wednesday before he is formally sentenced to death by a US federal judge, his lawyer said.

Defense lawyer Judy Clarke said he would speak of remorse for the April 2013 bombings, which killed three people and wounded 264 others in one of the bloodiest attacks on US soil since 9/11.

Tsarnaev had offered to plead guilty with a letter of apology last year, she added.