The army has been fighting rebels in the north for five years
Fighting in Yemen is reported to be continuing despite a conditional ceasefire called by the government in its conflict with northern Shia rebels.
The government had called the ceasefire to coincide with the end of the Muslim holy month of Ramadan.
The UN has appealed to both sides to allow humanitarian corridors to be opened so that aid can be delivered to those displaced by the fighting.
About 150,000 people have been displaced in the five-year conflict.
On Saturday, statements from both the military and the rebels accused the other side of continuing attacks in spite of the ceasefire.
The combat area has been cut off from journalists, and correspondents say it has been hard to verify conflicting reports from both sides.
It is the second recent ceasefire that appears to have quickly collapsed.
There has been growing concern about the fate of displaced people
The government had proposed that it begin late on Friday and run during Eid, the three-day holiday that starts on Sunday and marks the end of Ramadan.
The government's five conditions included removing road blocks, the withdrawal of rebel forces, the release of detained military personnel, and abiding by the constitution and Yemeni law in general.
But the rebels have asked that the ceasefire be unconditional.
The BBC's Paul Wood reports from Yemen that people at a camp for the displaced said rebels had been steadily winning territory from the army.
International concern about the conflict has intensified after witnesses said that more than 80 people were killed in a government air raid on a camp for displaced people on Wednesday.
The rebels, known as Houthis, complain of discrimination. They say they want greater autonomy and a greater role for their version of Shia Islam.
Both sides see unwelcome influences from abroad, with government accusing rebels of having Iranian backing and being accused itself of being influenced by Sunni-dominated Saudi Arabia.
The Yemeni government is also battling secessionists in the south and has been criticised by the US for its failure to tackle al-Qaeda militants in the east and pirates off the coast.