It also said wild tigers were facing the risk of extinction in some countries due to a lack of accurate information on their population.
"Poaching is the greatest threat to wild tigers today. Along with ivory and rhino horn, tiger parts are in high demand throughout Asia," WWF said in a release coinciding with Global Tiger Day.
It said that statistics from TRAFFIC, the wildlife trade monitoring network, show that a minimum of 1590 tigers were "seized" between January 2000 and April 2014.
"It is feared that countries not carrying out national tiger surveys could lose their tigers to poachers without realising. This may already be the case for some countries," it said.
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Currently, wild tiger numbers are known for India, Nepal and Russia which carry out regular national surveys. Numbers will soon be known for Bhutan, Bangladesh and China which are in the process of carrying out surveys.
Wild tiger populations for Malaysia, Indonesia, Thailand, Myanmar, Laos, Cambodia, and Vietnam are unknown, WWF said.
"This figure was just an estimate," Michael Baltzer, leader of WWF Tigers Alive Initiative, said.
"In 2010, many countries had not undertaken systematic national tiger surveys. Now many have or are doing so, but not all, leaving major, worrying gaps in our knowledge. Until we know how many tigers we have and where they are, we can't know how best to protect them," he said.