North Yemen has seen sporadic fighting for more than five years
Yemeni authorities have dismissed a ceasefire offer by northern rebels, insisting they must also agree to end attacks on Saudi Arabia, officials say.
Houthi rebels had said they would accept government truce terms if the Yemeni army first halted its offensive.
Several earlier ceasefires have broken down, some soon after being agreed.
Meanwhile some 20 rebels were killed in north-west Yemen amid renewed fighting between the sides, according to government sources.
The UN refugee agency says 250,000 Yemenis have been displaced by fighting in the region over the past five years.
Houthi rebels from the minority Shia Zaidi sect based in the north-western Saada district have been battling the government since 2004.
Rebel leader Abdul-Malik al-Houthi had earlier said he was willing to accept the government's conditions to avoid civilian casualties.
Mr Houthi offered to order his forces out of Saudi territory last week
"In order to avoid... the annihilation of civilians we reiterate our acceptance of the five points [for a ceasefire]," Mr Houthi said in an audio message posted on the internet.
These terms include a rebel withdrawal, the reopening of roads in the north, the release of all military and civilian prisoners and the return of captured equipment.
However Mr Houthi did not refer to a sixth condition Yemen is said to have added to the original ceasefire terms as a result of the rebels engaging in a cross-border conflict with Saudi forces.
"This is a key demand we cannot make concessions on," a spokesman for Yemen's ruling party told Reuters news agency.
The agency also quoted a Saudi military source saying rebel snipers were still crossing the border into Saudi territory and exchanging fire with Saudi troops on a daily basis.
Last Wednesday, Saudi deputy defence minister Prince Khalid bin Sultan said the rebels had been driven from Saudi land.