The United Nations High Commissioner for Human Rights has expressed "deep concern" over increasing attacks against civilians in Yemen with a total of 180 civilians killed in one month, raising the death toll to nearly 4000 since March 2015.

Cecile Pouilly at the UN agency said on Friday that August also marked an increase in the number of attacks against civilian facilities including hospitals, markets, and places of worship.

Her statement came only two days after airstrikes by the Saudi-led coalition bombed houses in the Red Sea port city of Hodeidah, killing at least 32 civilians.

Meanwhile, rebels known as Houthis have continued to tighten their siege on the city of Taiz, where they are fighting local forces aligned with the internationally-recognized government.