London: NATO must overhaul itself to be able to better defend its members from a potential Russian military threat, British Prime Minister David Cameron said on Saturday, He said the U.S.-led Atlantic alliance had to rethink its ties with Moscow because of the Ukraine crisis. Cameron, who is hosting a NATO summit in Wales next month, said he would use the event to push for the 28-member bloc to review its long-term relations with Russia to reflect the fact that Moscow sees NATO as an adversary. The British leader has been scathing about Russia`s annexation of Crimea and accused it of illegally arming pro-Russian separatists in eastern Ukraine, something Moscow denies. He has also sharply criticised Moscow`s response to the downing of a Malaysian airliner over Ukraine last month. NATO suspended all practical cooperation with Russia in April to protest against Moscow`s annexation of Crimea, but this did not include contact between the two at ambassadorial level or higher. In a letter to fellow alliance leaders and NATO Secretary General Anders Fogh Rasmussen, Cameron made it clear that the alliance needed to now go further. "Six months into the Russia-Ukraine crisis we must agree on long-term measures to strengthen our ability to respond quickly to any threat, to reassure those allies who fear for their own country’s security and to deter any Russian aggression," Cameron wrote, according to a text of the letter released by his office. He proposed drafting a new schedule of military exercises, building new infrastructure, pre-positioning equipment and supplies, and enhancing the NATO Response Force of up to 25,000 troops. "We must accept that the cooperation of recent years is not currently possible because of Russia’s own illegal actions in NATO`s neighbourhood, and revisit the principles that guide our relationship with Russia," Cameron wrote. A report by British lawmakers on Thursday accused NATO of being complacent about the threat that Russia posed, and said Baltic states Estonia, Lithuania and Latvia - all ex-Soviet republics ruled from Moscow - are particularly vulnerable. In response, NATO said it was already considering reinforcement measures and had acknowledged the need to adapt to a changed security environment. The alliance has stepped up exercises in eastern Europe since Russia annexed Ukraine`s Crimean Peninsula in March and has tripled the number of fighter jets based in the Baltics. On Monday, Britain said it would send 1,350 military personnel and more than 350 vehicles to Poland for a NATO exercise aimed at reassuring allies in eastern Europe worried that, after Ukraine, they could be the next target of Russian intervention. NATO`s top military commander, U.S. Air Force General Philip Breedlove, has said the alliance would have to consider permanently stationing troops in eastern Europe. Cameron, who is expected to meet Breedlove on Monday, said the alliance had to work out how to sustain "a robust presence" in the region for the foreseeable future.