The United Nations Refugee Agency (UNHCR) on Wednesday reported that an airstrike carried out by the US -backed Saudi-led coalition in Yemen killed 20 civilians-including women and children-who were fleeing violence in their home province.
Yemeni officials said several women and children were among the casualties.
"Preliminary reports are that the IDP (internally displaced) families were trying to flee hostilities from elsewhere in Taiz", a spokesperson said.
Yemen's government, allied with a Saudi-led Arab military coalition, has for years been battling Iran-backed Shiite Houthi rebels for control of the impoverished country.
"It also illustrates the difficulties in the delivery of humanitarian protection and assistance in Yemen", Spindler added.
Judges found that the Saudi-led coalition was "not deliberately targeting civilians" and alleged massacres were under investigation, concluding that it had not been established that there was "a clear risk that the items might be used in the commission of a serious violation of global humanitarian law".
Injuries were also reported, according to UNHCR, with a number of people taken to nearby hospitals.
The UN have said that the conflict is killing 75 people a day.
Saudi Foreign Minister Adel al-Jubeir told the Guardian that those figures were "vastly exaggerated".
Separately, UN officials said the coalition barred one of its flights to Yemen's Houthi-controlled capital, Sana'a.
The country has also been hit by a deadly conflict-induced cholera outbreak that has claimed more than 1,740 lives since late April.
Haq said the United Nations humanitarian air service had been allowed to take off on Wednesday and had landed in Sana'a carrying 26 humanitarian aid workers, but not the three journalists from the British Broadcasting Corporation.
The three BBC reporters were on the flight to cover the United Nations humanitarian operation, but Saudi Arabia warned the plane against taking off from Djibouti with any journalists on board.
The World Health Organisation estimates that more than 8,000 people have been killed in Yemen's conflict, a lot of them civilians, since the intervention.