Internal Affairs and Communications Minister Kazuhiro Haraguchi demanded Tuesday that Japan Post Service Co. give a written explanation by the end of the month about the significant delays in its parcel deliveries since last week.

Haraguchi told Japan Post Service President Shinichi Nabekura that he deplores "the fact that the delays caused trouble to many customers," while indicating the ministry may take disciplinary action against the company after receiving the explanation.

Separately, Nabekura told reporters he hopes the Yu-Pack delivery operations will return to normal as quickly as possible and be declared back on track by the end of Wednesday.

Japan Post Service, the main service arm of government-owned Japan Post Holdings Co., has said there were delays in delivery of a combined 320,000 parcels during the first five days since Thursday's integration of its operations with services run by a joint company set up in 2008 with trucking firm Nippon Express Co.

Haraguchi defended the government's decision to approve the integration in July, a traditionally busy month for the parcel delivery business, saying the joint company, JPEX, had amassed debts of ¥98 billion and the situation "could not be overlooked."