Vienna, Nov 5 : Austria's Interior Minister Karl Nehammer has admitted that a warning from Slovakia last summer about a gunman who went on the rampage in the centre of Vienna was not followed up. Four persons were fatally shot and 23 others wounded on Monday night. Asked about the revelations on Wednesday, Nehammer said the information had been investigated by the BVT domestic intelligence agency but no further action had been taken, the BBC reported. "Something obviously went wrong in communication," he told reporters, adding that he wanted an independent inquiry to find out why. Police in Slovakia revealed they had tipped off Austrian authorities about "suspects from Austria" trying to buy ammunition in July. Reports suggest the trip to buy bullets failed as the gunman had no licence. It has also emerged he was released early from a jail sentence last December for trying to join jihadists in Syria. According to German media, the 20-year-old, who was shot dead by police nine minutes after the attack began, travelled to neighbouring Slovakia to buy ammunition for a Kalashnikov AK-47 assault rifle but returned empty-handed. Slovak police said they had informed their Austrian colleagues immediately, adding they would not comment further. Among the 23 people wounded in the attack, 13 suffered bullet wounds and seven are in a serious condition. Most are from Austria, but some are from Germany, Slovakia, Luxembourg and other countries. One of those in a serious condition was also a student at the university of applied arts, known as Die Angewandte. Austrian authorities say the killer was armed with an automatic weapon, a pistol and a machete as well as a fake explosive belt. They were initially unsure if there had been more than one gunman, after Monday night's attack which lasted nine minutes across six crime scenes. But the interior minister confirmed on Wednesday that he had acted alone, as a review of videos received by police was now complete. Jihadist group Islamic State (IS) claimed on its propaganda outlet Amaq that it was behind the attack. /IANS