CAIRO — Airstrikes on a market and a farm in Yemen killed at least 68 civilians in a single day, including eight children, the United Nations said on Thursday.

The two attacks occurred on Tuesday, making it one of the bloodiest days for civilians so far in Yemen’s civil war. At least 109 civilians have been killed nationwide over the past two weeks, in a conflict that has intensified since the death of the country’s former president, Ali Abdullah Saleh, this month.

Local Yemeni officials blamed the Saudi-led coalition for the airstrikes.

More than three years of fighting have turned Yemen, which was already the poorest Arab country, into the world’s largest humanitarian crisis.

On one side are the Houthis, Shiite rebels aligned with Iran who took over the capital, Sana, in September 2014 and forced the internationally recognized government into exile. Those on the other side include an Arab coalition led by the Sunni kingdom of Saudi Arabia, which has waged a devastating air campaign since March 2015 to restore the government. So far, the conflict has only cemented a political deadlock.