QINGDAO - The deadly oil pipeline blasts in East China's Shandong province on Friday exposed severe problems of human error and "very serious dereliction of duty" was behind the accident, a senior official in charge of the country's work safety said Monday.

Yang Dongliang, director of the State Administration of Work Safety and head of an investigation team for the accident, said the accident exposed three severe problems: the unreasonable layout of oil pipelines and urban drainage pipes, negligence of duty in pipeline supervision, and unprofessional handling of oil leakage prior to the blasts.

Yang made the remarks in Qingdao City at a meeting of the investigation team for the accident, which had left 55 people dead, nine missing and 136 hospitalized as of Monday morning.

The State Council has invited staff of the Supreme People's Procuratorate to join the investigation.

Yang requested that the investigation team speed up the investigation and publicize the report in a timely manner in order to give the public a sincere and responsible explanation.

At the meeting, Yang conveyed the spirit of President Xi Jinping's speech made Sunday in Qingdao, ordering relevant authorities to carry out a special campaign nationwide to ensure the safety of oil and gas pipelines as well as city pipelines.

On Sunday afternoon, President Xi visited some of the injured people and medical staff in the Huangdao branch of the hospital affiliated with the Medical College of Qingdao University. He also offered condolences to the family members of victims who died in the accident.

Xi stressed that a lesson should be drawn and work safety responsibilities should be fulfilled to avoid similar accidents.