Yemeni Houthi forces on Wednesday accused the Saudi-led coalition operation in the country of violating a UN-backed ceasefire that began on Tuesday.
The United Nations spokesman Ahmad Fawzi announced the ceasefire on Tuesday, stating that it is an outcome of peace talks that were underway in Switzerland.
According to the UN, at least 5,800 people have been killed in the ongoing civil war in Yemen, nearly half of them civilians, and more than 27,000 have been injured since March.
The truce was set to continue up until the 21st of December, and was to be renewed automatically with the commitment of both parties.
As a result of a Houthi advance, Yemeni President Abd Rabbuh Mansour Hadi had to temporarily move to the Saudi capital Riyadh, and formally requested the Arab states help "save Yemen" from the Houthis.
Since late March a Saudi-led coalition has been fighting against the Iranian-backed Houthis to restore Hadi to power.
Brigadier General Sharaf Luqman, a spokesman for Yemeni forces loyal to former president Ali Abdullah Saleh said a "serious escalation by land, sea and air is taking place by the alliance in various areas," according to the Houthi-controlled Saba news agency, a claim Saudi Arabia rejected.
The spokesman said the Saudi-led coalition is attacking Houthi forces in the Red Sea port cities of Hodaida and Taiz.
"We will not stay hand-tied but we will respond strongly towards the breaches that are taking place by the alliance and their mercenaries," Luqman said.
According to the Saudi al-Riyadh daily, the Saudi-led coalition's spokesman, Brigadier General Ahmed al Assiri, said the coalition is committed to the ceasefire but is ready to respond to any attack.