(VIDEO) BBC Gaza correspondent Alan Johnston appeared in a video posted on the Internet on Sunday wearing what he said was an explosive belt which his captors have threatened to blow up if force was used to free him. "The situation now is very serious. As you can see I have been dressed in what is an explosive belt, which the kidnappers say will be detonated if there was any attempt to storm this area," Johnston said in the video posted by the Army of Islam on a website used by militants. Johnston appeared wearing a white and blue belt around his torso with black shoulder straps over a dark red sweater in the undated video filmed against a black background. The 45-year-old Briton looked tired, but unharmed. He said negotiations to seek his release were thwarted by what his captors told him was a plan by Britain and Palestinian group Hamas to use force to secure his release. "Captors tell me that very promising negotiations were ruined when the Hamas movement and the British government decided to press for a military solution to this kidnapping." Ismail Haniyeh, the prime minister of the Hamas-led government sacked by Palestinian President Mahmoud Abbas of Fatah, said earlier on Sunday his group has not used force to free Johnston at the request of the British government, fearing he might be killed or injured in the process. Hamas officials in the Gaza Strip say they are pressing the kidnappers to free Johnston. The BBC journalist went missing in Gaza on March 12 and is believed to be being held by the little known group that appears to draw inspiration from al Qaeda but also seems to be linked to violent clan rivalries among Gaza's 1.5 million people. Johnston's captors have demanded Britain free Muslim prisoners, particularly Islamist cleric Abu Qatada, in exchange for his release.