Rebels in northern Yemen are reported to have released 178 civilians and government soldiers.
The release comes after the Yemeni government accused the rebels of not fully complying with a ceasefire agreed in February.
The rebels, known as Houthis, had fought Yemeni forces since 2004, until a major offensive by the government last year led to the peace deal.
But the deal is still very fragile because of mistrust on both sides.
Under the terms of the deal, the rebels agreed to free all prisoners.
They also pledged to open up roads and withdraw from government buildings and army posts in the rebel areas in northern Saada province.
But rebels have also demanded the return of their own prisoners held by the government in Sanaa, which seems an unlikely prospect.
Many of the hundreds of rebel prisoners have been convicted by courts, some have been given death sentences and the government may refuse to let them go.
For months the Houthis fought both Yemeni and Saudi troops after they made an incursion over the Saudi border last November.
The rebels, called Houthis after their leaders' family name, attacked Saudi Arabia after accusing the government there of aiding the Yemen government in suppressing them.
The rebels are from the Zaidi Shia Islamic sect, a minority in Yemen but the majority in parts of the north, and say they want more autonomy for their region.
The government of Yemen is also facing two other militant groups - al-Qaeda and southern secessionists.
South and North Yemen were united in 1990 and fought a brief civil war in 1994, and grievances with separatists still remain.
The truce with the Houthis in northern Yemen has allowed the government in Sanaa to turn its attention to the secessionist movement and to the al-Qaeda cadre said to be hiding out in the same area.
Elsewhere in the country security around oil infrastructures has been tightened following warnings of a possible revenge attack by al-Qaeda in the Arabian Peninsula.
The government killed three top al-Qaeda operatives in bombing raids this week.