LONDON (AFP) - London's police said they were prepared for the possibility of bomb threats and attacks targeting the Wimbledon tennis championships as the tournament got under way Monday. Superintendent Pete Dobson, the day-to-day police commander at the All England Club, said their plans for policing the championships had to be set against the national threat levels posed by international and Irish republican terrorism. He stressed that no specific threats had been made against the tournament but London's police were nonetheless on alert. "The tennis championships are one of the great sporting events of the year," Dobson said. "We have road-tested plans to ensure we have a safe and secure event for all to enjoy. "The threat level we are facing from international terrorism is at severe, only at one level away from the top level, critical," he explained. "Irish republican terrorism is at substantial. That means we have to be prepared for the possibility of an attack. London did receive a coded bomb threat on May 16, so our plans include the possibility of receiving associated bomb threats." That threat from Irish republican paramilitaries came on the eve of an historic trip to Ireland by Queen Elizabeth II. "I've got a number of officers that respond to unattended packages that become suspicious," Dobson said. "Then we have specific arrangements that would involve properly-trained explosives officers that would be able to attend within a very short period of time -- no different to most locations in London." Dobson would not disclose how many officers are on duty at the championships for security reasons, but said they were prepared in case the threat level went up to critical. "We have to raise our game one notch. We have plans in reserve that should the threat level increase, we can bring them into play. They would overt," he said. "It would have implications for the way the championships are run because it would cause some disruption but it would be short of stopping the championships altogether." Police officers are also on the look-out for stalkers.