"A young protester who had torn the flag of the MPS (Deby's ruling Patriotic Salvation Movement) was shot dead," during the protest which had been banned by the government, the police officer said yesterday on condition of anonymity.
Opposition leader Saleh Kebzabo confirmed the news, saying one person had died after being shot by live police rounds during the authorities' attempts to disperse the protesters.
He added that another youth had been hit in the chest by a bullet and taken to hospital.
Kebzabo said many of the protesters were "very angry at being prevented from marching" and had returned only for their protest to be broken up again.
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However a small group returned to the fray and "things degenerated" he added.
Chad has banned opposition rallies ahead of today's swearing-in ceremony for Deby.
The opposition has called for Deby's re-election in April to be annulled, citing voting irregularities.
Deby, 64, who came to power in 1990, was re-elected in a first round vote in April with 61.5 percent of ballots cast against 12.8 percent for his nearest rival Kebzabo, according to official results.