The massive truck bomb that killed 15 people, including a Kenyan diplomat, and wrecked Somalia’s premier hotel has stunned the capital and raised fears Monday that the Islamic extremist al-Shabab rebels are escalating their violence. Senior police official Capt. Mohammed Hussein said the toll has risen to 15. “This is a very worrying situation,” he said as he stood outside the Hotel Jazeera near a dead body. “This happened despite all the security precautions in place.” In a visit to neighboring Ethiopia, US President Barack Obama said Monday the bombing is a reminder “we have more work to do” in stemming terrorism in the region and that groups like al-Shabab offer nothing but destruction.