Clashes have been reported in Yemen even as a truce between Shia Houthi rebels and Saudi-backed pro-government forces took effect.
Witnesses said that rebel artillery pounded residential areas near the city of Taiz, reported the BBC.
On Saturday, the Saudi-led coalition had said that it would stop air raids at midnight for five days to allow the much-needed humanitarian aid in, adding that it reserved the right to respond to 'military activity or movement' by Houthi rebels.
A Houthi spokesman had said that the rebels would not adopt a position on the move unless they were officially informed.
The unexpected ceasefire was announced after Yemen's President Abdrabbuh Mansour Hadi wrote to Saudi's King Salman, asking for a break to allow humanitarian supplies to be delivered.
The shelling came days after Saudi-led coalition strikes killed 120 people, including civilians, in Taiz province.