LONDON, Jan 14 (Reuters) - British Prime Minister Boris Johnson and Turkey"s President, Tayyip Erdogan, discussed on Friday their significant concern over the build up of Russian troops on Ukraine"s border. "They shared significant concerns about the build-up of Russian troops on Ukraine"s border, and emphasised NATO"s collective resolve to avoid further escalation," a statement from London on the talks said. "They committed to continue working through NATO to reach a resolution." The two leaders also discussed further strengthening their bilateral security and defence cooperation, and a desire to boost trade and investment.