Quetta, April 22 : Four people were killed and over a dozen others injured when an explosive-laden vehicle exploded inside the parking lot of a hotel in Pakistan's Quetta city, Interior Minister Sheikh Rasheed Ahmad confirmed. There was a threat alert in Quetta and other major cities after some suspicious calls were intercepted, and security was on high alert including cities in Balochistan, Rasheed told Xinhua news agency on Wednesday night. He said that despite the security measures, the vehicle carrying explosives managed to enter the parking lot from the main gate of the Serena hotel, which is a matter of big concern and the responsible people will be taken to task for creating security lapse which gave terrorists a chance to carry out the attack. Terror group Tehrik-i-Taliban Pakistan claimed responsibility in a text message to journalists saying a suicide bomber launched the attack targeting locals and foreigners, but the claim has not yet been officially confirmed. The injured were shifted to Civil Hospital whose spokesman Waseem Baig told Xinhua that two of the injured people are in critical condition and a state of emergency has been declared at the hospital by the provincial government. Soon after the blast, the hotel's parking area located in its premises was sealed by the counter terrorism department of police who also restricted media to access the site for reporting, Inspector General Police of Balochistan Muhammad Tahir Rai said. According to initial investigation, some 40 kg of explosives were used in the attack. Fire erupted in several vehicles following the blast, badly destroying five to seven of them, he added. Talking to Xinhua, intelligence sources, who were close to the hotel when the incident happened, said that the loud blast was heard many miles away from the blast site and fire erupted in the hotel's parking following the explosion. Security has been beefed up in other cities including Islamabad following the blast and all sensitive government buildings and installations are being guarded, according to local reports. /IANS