Efforts to save the endangered tiger are being undermined by a lack of knowledge as to how many remain in the wild, according to an animal conservation group.

To mark International Tiger Day WWF is calling on countries across Asia to improve the quality of data available regarding tiger populations. 

In 2010, a "tiger summit" in St Petersburg, Russia, set the goal of doubling the number of wild tigers by 2022, against a baseline population believed at the time to be as few as 3,200.

"This figure was just an estimate” said Michael Baltzer, head of WWF's Tigers Alive Initiative.

"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 added. 

WWF praised India, Nepal and Russia for carrying out regular national surveys that gave a reliable indicator of their tiger populations.

Bhutan, Bangladesh and China will shortly release the results from their own surveys, it said.

On the other hand, "wild tiger populations for Malaysia, Indonesia, Thailand, Myanmar, Laos, Cambodia and Vietnam are unknown," it said.

WWF called on these countries to carry out their surveys urgently.

"Systematic national surveys take six-12 months to plan and a minimum of a year to complete, so these surveys must start now if an updated global tiger figure is to be released" in 2016, the halfway point to 2022, it said.

Tiger populations have been rapidly decreasing over the past century due to trophy hunting, poaching and habitat loss.