SANAA, Oct. 21 (Xinhua) -- Yemen's dominant Shiite Houthi group traded accusations with Saudi Arabia on Friday over breaching a ceasefire mediated by the United Nations, deepening the uncertainty of the peace process in the country.
The UN-brokered 72-hour ceasefire, meant to last for three days, came into effect on Wednesday midnight.
According to a statement released by Houthi-run media, a Thursday night air strike by the Saudi-led coalition killed three civilians in the northern province of Saada.
The coalition accused the Houthis of firing rockets on the southern Saudi cities of Jazan and Najran, killing two civilians, according to a statement by Saudi official media.
Meanwhile, Saudi-backed Yemeni government of exiled President Abd-Rabbu Mansour Hadi said its troops in the Yemeni central province of Marib shot down three missiles fired by Houthis late on Thursday.
The ceasefire is aimed at facilitating humanitarian aid supplies to the war-stricken cities.
UN officials hoped the truce would be extended to pave the way for resuming stalled peace talks and to end the war.
Previous attempts to cease fire between warring parties in Yemen had hardly been observed, with all sides involved in the conflict trading accusations of violating the truce.
Ceasefires backed by the UN are frequently interrupted.
On March. 23, Ismail Ould Cheikh Ahmed, special envoy of the UN secretary-general for Yemen, announced that a nationwide ceasefire in Yemen was scheduled to begin in April, and peace talks scheduled to begin in Kuwait.
However, the Houthis accused Saudi-led coalition warplanes of killing seven Houthi followers in the Houthi-held capital Sanaa on May 8, which triggered the Houthi and Saleh delegations to walk out of the talks in protest.
A day later, the warring parties came back to the peace table in Kuwait and in June the UN special envoy said that "after extensive discussions with the participants, the main principles that will guide the next phase of Yemeni talks had been established."
Talks continued while Houthi group and the Saudi-led coalition accused each other of violating the ceasefires.
On Oct. 17, the UN declared that a 72-hour ceasefire between Houthi fighters and their rival Saudi-backed exiled government forces will take effect at 2359 local time (2059 GMT) on Oct. 19.
However, the ceasefire became fragile after the warring sides traded accusations of breaching it.
The conflict in Yemen began after Arab-spring style 2011 mass protests that eventually forced former President Ali Abdullah Saleh out of power.
The Houthis, supported by Saleh, seized the Yemeni capital Sana'a and some other Yemeni cities in September 2014, forcing President Abd-Rabbu Mansour Hadi and his government into exile.
The Houthis and their ally forces loyal to Saleh have controlled most of Yemen's northern regions since September 2014, while the Saudi-backed Hadi's government has worked with its tribal allies in the southern provinces they recaptured from Houthi rebels.
The Saudi-led coalition intervened in Yemen's conflict in March 2015 with an air force campaign to restore Hadi to the power and roll back Houthi gains.
The 19-month civil war has killed over 10,000 people, mostly civilians.