Two explosions rocked a counter-terrorism ammunition depot in northwest Pakistan on Monday. Here are what we know so far:At least 13 people were killed and over 50 injured on Monday in two explosions at a counter-terrorism ammunition depot in northwest Pakistan, police officials said.The explosions occurred at the counter-terrorism office in Swat valley, an area that was previously controlled by Islamist militants before a military operation in 2009.Most of those killed in the blasts were police counter-terrorism officers, a police official said, adding that a woman and her child who were passing by the building were also killed.On Twitter, prime minister Shehbaz Sharif initially described Monday’s blasts as a ‘suicide attack’. “Our police has been the first line of defence against terrorism,” he tweeted. Late at night he tweeted an update saying “The nature of the blast is being investigated”.The cause of the explosions is still being investigated. A police spokesman said that ammunition caught fire, likely due to an electric short-circuit.Since the start of the year, two attacks on large police bases have been linked to the Pakistani Taliban, known as Tehreek-e-Taliban Pakistan (TTP).The valley has a significant presence of Pakistani police and military counter-terrorism staff, as it has been prone to insurgency.The Tehreek-e-Taliban Pakistan (TTP), a Pakistani Taliban branch, has claimed responsibility for several recent attacks on police in Pakistan, accusing them of extrajudicial executions.Since the Taliban takeover of Kabul, Pakistan has witnessed a significant increase in attacks in its border regions with Afghanistan, with Islamabad alleging that offensives are being launched from Afghan soil.The TTP was founded in 2007, when Pakistani militants fighting alongside the Taliban in Afghanistan splintered off to focus attacks on Islamabad as payback for supporting the US invasion after the 9/11 attacks.(With inputs from agencies)