Airstrikes and ground battles were reported in Yemen on Saturday within hours of a ceasefire coming into effect. Reports from the port city of Aden also indicated that Houthi forces fired mortars and rockets at opposition fighters in the city and airport.

Air bombing from the Arab-led international coalition hit the capital Sanaa and Yemen's third-largest city Taiz early Saturday, followed by reports of ground fighting between Shia Houthi militants that control large swaths of the country and rival forces in Taiz, the Associated Press reported. Both sides blamed the other for initiating the fighting.

The U.N.-brokered ceasefire, which took effect on Friday at 11:59 p.m., local time, was set to last throughout the Muslim holy month of Ramadan to allow humanitarian agencies to deliver sorely needed aid to the embattled country.

Saudi-led coalition spokesman Brigadier General Ahmed Asseri told Al Jazeera that the coalition needed more information about the breaches that had occurred, and urged the Houthis to respect the truce. Houthi leader Abdelmalik al-Houthi also called for the ceasefire to be respected by "the regime and their mercenaries."

A previous ceasefire was declared in May, during which humanitarian supplies and assistance were sent to Yemen. However, aid workers and international groups warn that the country's civilian population is suffering under growing shortages of food, electricity and medical supplies, with over 80 percent of the people believed to be in need of emergency aid.

U.N. Secretary General Ban Ki-moon said earlier in the month that the conflict was a "catastrophe" and urged the parties to reach a solution quickly.

The Iran-allied Houthis control large parts of the country's north, including the capital, after they displaced the internationally recognized President Abed Rabbo Mansour Hadi. Hadi fled the country in March, and his government-in-exile is based out of Riyadh. The Arab-led coalition has called for the Houthis' immediate surrender and the restoration of Hadi's government.

Fighting and bombings have resulted in over 3,000 deaths in Yemen since the conflict began in March. All parties had welcomed the truce and called for its extension. After Saturday's events, a Houthi military official said it was unlikely that any calm would last.

"The Saudi aggression, with these violations, confirms that it will persist with its aggression on Yemen and won't carry through on its pledges to the United Nations," the official told Houthi-controlled news agency Saba, cited by Al Jazeera.