The rebels oppose Yemen's close alliance with the United States and the government says they want to install an Islamist government.
''We renew our call to straying elements to surrender and hand in their weapons to the state,'' said Saleh in a televised speech marking the unity between northern and southern Yemen.
''We guarantee that they will receive a fair trial for committing war crimes against citizens and soldiers.'' Thousands of people have fled their homes in the latest bout of the conflict, which has been raging on and off since 2004.
Sunnis make up most of Yemen's 19 million people, and most of the rest belong to the Zaidi branch of Shi'ite Islam.
The government of Sunni-dominated Yemen accuses the rebels, led by Abdul Malik al-Houthi, of seeking Islamist rule. The rebels say they are defending their villages against what they call government aggression.
Yemen, the ancestral homeland of al Qaeda leader Osama bin Laden, joined the US-led war on terrorism after the September. 11 attacks on US cities. Houthi's backers are not linked to al Qaeda.