Scattered clashes between rebels and pro-government forces undermined a fragile ceasefire in Yemen Thursday as global pressure intensified for a lasting truce in a country where millions are homeless and hungry.
The ceasefire, for an initial period of three days, took effect shortly before midnight on Wednesday under a United Nations plan which aims to allow sorely needed aid to reach suffering civilians.
A Saudi-led Arab coalition intervened in March 2015 to support the government of President Abedrabbo Mansour Hadi after rebels overran much of Yemen.
Saudi Arabia and Washington accuse Iran of arming the insurgents, charges Tehran denies.
Coalition spokesman Major General Ahmed Assiri told Al-Ekhbariya state television that there had been "a certain number of violations" of the ceasefire.
If they continue, he said, the coalition "will take appropriate measures."
Yemeni residents said they have had enough of failed truces.
"We want a lasting ceasefire," said Sadok Abdullah, 28, a resident of rebel-held Sanaa.
"They're mocking us with a three-day truce," said Ali al-Doush, a 32-year-old civil servant who has not been paid for three months.
"We want an end to the war."
Shortly after the truce began, the coalition said it "will abide by the ceasefire", which aims for "distribution of the greatest possible humanitarian and medical assistance" to Yemen's people, especially besieged third city Taez.
It said it will continue an air and maritime embargo, to prevent weapons shipments to the rebels, and will maintain airborne reconnaissance.
The rebels' military spokesman, General Sharaf Lokman, said his forces will respect the ceasefire as long as "the enemy" also abides by it.
However, he urged his fighters to be ready to retaliate against "all aggression."
A spokesman for pro-government forces also declared "respect for the truce" but reserved the right to respond to violations.
Pro-Hadi forces said in a statement they recorded nine violations by the rebel Huthis and their allies after midnight in Nahm, northeast of Sanaa.
Three pro-government fighters were killed near the Red Sea in Hajja province when rebels, after midnight, began a counter-offensive to retake positions lost before the truce, a loyalist officer, Colonel Abdel Ghani al-Chebli, told AFP.
"The rebels didn't respect earlier truces and we have orders to retaliate. We are in a defensive position," he said.
Military sources and residents said there had also been fighting around Taez, and pro-Hadi positions came under fire in Sarwah, east of Sanaa.
In the immediate aftermath of a ceasefire, it can be difficult to silence every single weapon.
Civilians have paid the highest price in the war.
Almost 6,900 people have been killed -- more than half of them civilians -- while another three million are displaced and millions more need food aid.
EU foreign policy chief Federica Mogherini late Wednesday said the truce should be a first step towards resuming UN-led peace talks.
"The ceasefire must be respected by all sides and its duration extended so as to create the necessary conditions for such negotiations," she said.
Mogherini added the ceasefire will allow urgent humanitarian assistance to reach large parts of the population that have suffered drastic shortages.
On Tuesday, US Secretary of State John Kerry said the truce "requires all parties to implement a full and comprehensive halt to military activities of any kind, and help facilitate the delivery of humanitarian assistance."
The last ceasefire attempt began in April and later collapsed alongside UN-brokered peace talks in Kuwait.
Fighting escalated after those talks ended unsuccessfully in August, until an October 8 coalition air strike which the UN said killed more than 140 people and wounded at least 525 at a funeral in Sanaa.
The United States announced an "immediate review" of its intelligence and refuelling assistance to the coalition, whose investigative team then released unusually quick findings from a probe of the incident saying the funeral was "wrongly targeted".
In another major development, the US Navy for the first time targeted rebels directly.
On October 13 it hit radar sites which, the US said, were involved in missile launches against a US warship and other vessels.
Yemen's Houthi rebels are allied with members of forces loyal to ex-president Ali Abdullah Saleh.
The UN's humanitarian coordinator for Yemen, Jamie McGoldrick, on Wednesday told reporters he hoped the truce will provide a chance for aid workers to reach areas isolated by the fighting.
"We're seeing very high levels of malnutrition and food insecurity," he said.
The truce does not apply to militants who have exploited the conflict to gain ground in the south.
Suspected Al-Qaeda militants on Thursday attacked a loyalist security checkpoint in the southern province of Abyan, killing four soldiers and wounding two, a security official said.
One of the attackers was killed and another wounded in ensuing clashes.