The leader of the Scottish Conservatives has threatened to withdraw her party's support for the SNP's flagship education policy.

Ruth Davidson told MSPs at Holyrood on Thursday that her party may "withdraw" their support for the curriculum for excellence in the wake of new statistics showing a decline in education standards in Scotland.

The Pisa survey released on Tuesday showed Scotland slipping down the international league tables with its worst performance since the study began in 2000.

The Curriculum for Excellence was introduced in 2010 followed by the replacement of Standard Grades in 2013 and a new Higher qualification the following year.

Davidson told Nicola Sturgeon at First Minister's Questions that the policy must now go on "probation".

She told MSPs: "The single biggest educational reform under this SNP government has been Curriculum for Excellence.

"And nobody here can simply brush aside the fact that since it has come in standards have fallen.

"I am telling the First Minister today that our ongoing support for Curriculum for Excellence cannot be taken for granted. I believe that this entire project should be put on probation."

The First Minister defended the SNP government's education reforms, describing the principles behind them as "absolutely right".

Earlier in the session, Sturgeon said she takes "responsibility on behalf of the Scottish Government" for the performance of the country's education system.

The First Minister said: "There are lots of other evidence I could cite about Scottish education but I am not going to do that today because the results of the Pisa survey earlier this week are not where I want us to be.

"They are not good enough and I am determined that we will take the action that will lead to improvements."

The Scottish Government plans to make further reforms to the country's education system with an aim of making schools more autonomous from local government.

Education secretary John Swinney has already began to implement a system of national standardised assessments.

The first data from these will be published by the devolved administration next week.

Sturgeon said these reforms will be "controversial" and will be "met by resistance".

The First Minister said it will be "interesting" to see whether the opposition is in support of her government or not.