UNITED NATIONS, July 11 (Xinhua) -- UN Secretary-General Antonio Guterres strongly condemns the resumption of attacks on civilian vessels in the Red Sea by the Houthis in Yemen, said his spokesman on Friday.

The sinking of two commercial vessels, along with the deaths of at least four crew members and injuries to others, is a dangerous re-escalation in this critical waterway, said spokesman Stephane Dujarric in a statement.

With at least 15 crew members reported missing, Guterres calls on the Houthis not to take any actions that impede the ongoing search-and-rescue operations for the missing crew, said the spokesman.

"Beyond being an unacceptable attack on the safety and security of seafarers, these acts also violated the freedom of navigation, caused a hazard to maritime transport and represent a serious risk of significant environmental, economic and humanitarian damage to an already vulnerable coastal environment," said Dujarric.

Guterres emphasizes that international law must be respected by all parties at all times, he added.

The UN remains committed to continuing its efforts toward broader de-escalation in the region as well as continued engagement with Yemeni, regional and international actors to secure a sustainable and peaceful resolution to the conflict in Yemen, said the spokesman. ■