Nine civilians were killed and at least 13 wounded earlier this week in attacks in the provinces of Hodeidah and Hajjah in war-torn Yemen, the UN said on Friday.
In Hodeidah, eight people were killed and 10 were wounded Tuesday when an artillery shell hit a market to the west of the Tuhayta district, according to a statement by the UN Office for the Coordination of Humanitarian Affairs.
The statement added that unconfirmed reports indicated a woman was killed and three children injured the next day when a house was hit in the northern province of Hajjah.
"These attack are unconscionable," said the United Nations' humanitarian coordinator for Yemen, Lise Grande.
"The country is facing the worst food security crisis in the world and yet the killing continues. Parties to the conflict are obliged to do everything possible to protect civilians."
She did not name the parties behind the attacks.
The statement said there have been 271 civilian casualties, including 96 fatalities, between January 1 and February 14 in Yemen.
More than 24 million Yemenis, more than three quarters of the country's population, are now dependent on some form of aid for survival, according to the UN.
The Iran-backed Huthi rebels have battled a pro-government military coalition, led by Saudi Arabia and the United Arab Emirates, for control of the impoverished country for four years.
Both parties are accused of failing to protect civilians in the conflict, described by the UN as the world's worst humanitarian crisis.
Around 10,000 people -- mostly civilians -- have been killed and more than 60,000 wounded in the conflict, according to the World Health Organization.
Human rights groups say the real figure could be five times as high.