The IMF has warned Brexit could deal the British economy a "negative and substantial" blow as Vladimir Putin suggested David Cameron was trying to "blackmail" Europe with the EU referendum.
Meanwhile The Times newspaper came out Saturday in favour of Britain staying in the European Union, five days ahead of the vote on whether the UK should stay in the bloc or leave.
The pound rallied as investors leaned towards a 'Remain' outcome from Thursday's closely-contested referendum.
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Cox, who was backing the 'Remain' campaign, was slain in her northern English constituency on Thursday.
Murder suspect Thomas Mair has been charged and was to appear in a London court on Saturday.
With less than a week until the referendum, the International Monetary Fund warned that a so-called Brexit would harm the British economy while "contagion effects" could hit markets worldwide.
In the worst-case scenario, the UK economy would sink into recession next year and overall economic output would be 5.6% lower than otherwise forecast by 2019, with unemployment rising back above 6%, it said Friday.
"While there is much uncertainty about the precise economic effects of an exit from the EU, they are likely negative and substantial," the Washington-based global crisis lender revealed in its annual British economic check-up.
"An exit would precipitate a protracted period of heightened uncertainty that could weigh on confidence and investment and increase financial market volatility."
In addition, "contagion effects could result in spillovers to regional and global markets, although the primary impact would be felt domestically".
While in a "limited impact" scenario the IMF said the economy would only lose 1.4% from the current outlook by 2019, the report gave one of the starkest pictures yet of the impact of Brexit.
Meanwhile Russian President Vladimir Putin suggested British Prime Minister David Cameron had called the referendum to "blackmail" and "scare" Europe.
"Why has he set up this referendum? To blackmail Europe? Or to scare it? What is the purpose if he himself is against" Britain leaving the EU, Putin said Friday during a meeting with representatives of news agencies.
"Some experts say a Brexit will be to the detriment of Europe. But others say that the EU will be more stable," Putin said, pointing to the example of British fishermen.
"They explain how hard it is to live with the restrictions on fishing. But there are advantages in other sectors," he added.