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British Prime Minister David Cameron said Monday that the gunman behind last week's massacre in Sousse, Tunisia, declared war on Britain when he shot and killed at least 30 Britons.

Cameron said the government will provide a "full spectrum" response, including helping security forces in Tunisia track down any accomplices, The Guardian reports. Cameron said the government would not ramp up travel advisories to Tunisian coastal resorts for now, saying the killer wanted to destroy the tourist industry, which accounts for 15 percent of the country's economy. He also said that soon, his government will publish a new counter-extremism strategy that will likely ban several organizations deemed to be radical and suppress extremist messages online and on television stations.

Cameron announced that on Tuesday and Wednesday, a major exercise will take place in London to test the country's readiness for a terrorist attack. "We are a target," Cameron told BBC Radio 4's Today program. "Frankly, we cannot hide from this thinking that if you step back you become less of a target. They are attacking our way of life and what we stand for, and so we have to stand united with those that share our values."