GENEVA, May 11 (Xinhua) -- April was the deadliest month for civilians in Yemen this year, with at least 236 civilians killed and 238 others injured, a sharp increase from the preceding month, the Office of the UN High Commissioner for Human Rights (UNHCHR) said Friday.

UN rights office spokesperson, Ravina Shamdasani, said at a UN briefing here that the total number of 474 civilian casualties during the month was well over double the 180 civilian casualties documented in March this year and is "deeply" concerning.

In the first week of May, the heavy toll continued, with 63 civilian casualties documented by the UN Human Rights Office in Yemen, including six deaths and 57 people injured.

"Recent attacks against sites located in densely populated areas, including Monday's airstrikes against the presidential office in Sana'a raise serious doubts about respect for the principles of precaution, distinction and proportionality in international humanitarian law," said Shamdasani.

Based on the information collected by the UN rights office, the first raid directly hit the presidential office, located in a densely populated area.

"Eyewitnesses told us that the same building was hit again about seven minutes after the first strike, causing additional casualties among the first responders to the first strike," said the UNHCHR spokesperson.

In another recent incident, 24 civilians were killed, and 13 others injured in an airstrike by the Saudi-led collation against a gas station in Hajjah Governorate.

The coalition intervened in the Yemeni conflict in March 2015 to roll back the Iranian-allied Shiite Houthi rebels and support the internationally-recognized government of President Abd-Rabbu Mansour Hadi.

The rebels have seized control over much of the country's north since September 2014, including the capital Sanaa, and forced President Hadi and his government into exile in Riyadh, the capital city of Saudi Arabia.

The war has killed more than 10,000 Yemenis, mostly civilians, and displaced 3 million others, triggering one of the world's worst humanitarian crises.

"We have also documented casualties resulting from apparent indiscriminate shelling by the Houthis, including recent incidents on 1 and 2 May, during which five civilians were injured and one killed," said Shamdasani.