Bildt added that he expected China to "react strongly" to the nuclear test, which North Korea confirmed following initial reports of seismic activity at the same location of previous nuclear tests carried out by the regime in Pyongyang.
The official KCNS news agency reported that North Korea had used a miniaturized and lighter nuclear device with greater explosive force than previously.
United Nations Secretary General Ban Ki-moon also condemned the test as "deplorable", criticizing North Korea for defying "strong and unequivocal" calls to refrain from "provocative measures".
In addition to issuing a condemnation, Bildt added that he was cancelling a planned courtesy visit scheduled for Tuesday with North Korea's ambassador to Sweden
"Instead he will probably be called in at a lower level in order to receive a protest," Bildt told the TT news agency.