BAB AL-HAWA, Syria -- World Health Organization chief Tedros Adhanom Ghebreyesus visited rebel-held northwestern Syria on Wednesday, his first trip to areas outside Damascus's control since a devastating quake last month, an AFP correspondent reported. Tedros was the highest-ranking United Nations official to visit the rebel-held zones since the February 6 quake. He entered from neighbouring Turkey via the Bab al-Hawa crossing and visited several hospitals and a shelter for those displaced, the correspondent said. The Bab al-Hawa crossing is located in the Idlib region, which UN officials rarely visit and is controlled by the jihadist group Hayat Tahrir al-Sham. In the aftermath of the quake, activists and emergency teams in the rebel-held northwest decried the UN's slow response, contrasting it with the planeloads of humanitarian aid that have been delivered to government-controlled airports. UN relief chief Martin Griffiths admitted on February 12 that the body had "so far failed the people in northwest Syria". A total of 420 trucks loaded with UN aid have crossed into the rebel-held pocket since the tragedy. More than four million people live in areas outside government control in Syria's north and northwest, 90 percent of whom depend on aid to survive. Tedros's trip comes after he met President Bashar al-Assad in Damascus on February 12. The 7.8-magnitude quake that struck war-torn Syria and Turkey killed more than 50,000 people across the two countries. The Syrian government has said 1,414 people were killed in areas under its control, while Turkish-backed officials in Syria have put the death toll in rebel-held areas at 4,537.