At least six people have died in protest-related violence as supporters seeking Imran Khan’s release from prison broke through barriers meant to lock down Islamabad.

Thousands of opposition protesters have converged on Pakistan's heavily-barricaded capital, demanding the release of jailed former prime minister Imran Khan.

Supporters of the ex-prime minister marched toward Islamabad, the capital. Clashes with the police left at least one officer dead, the authorities said.