MEXICO CITY - THE investment firm owned by Mexican billionaire Carlos Slim has purchased a one per cent stake in Citigroup, the financial giant recently rescued by the US government, an analyst close to the transaction said Tuesday.

The stake - amounting to around 26 million shares, worth around US$150 billion (S$226 billion) - is 'a portfolio investment of Grupo Financiero Inbursa,' the analyst told AFP, requesting anonymity.

The US government's more than 300-billion-dollar rescue of Citigroup late Sunday sparked a frenzy on the markets, with Wall Street and European stock markets soaring as investors cheered the news.

The deal leaves Washington with the burden of the bank's potential losses of up to US$306 billion and responsibility to inject capital of US$20 billion, which follows a previous US$25-billion-dollar infusion.

US-based Citi operates in more than 100 countries and, with more than two trillion dollars in assets, is widely viewed as too big to be allowed to fail.

Slim, a Mexican businessman largely focused on the telecommunications industry, was ranked second richest person in the world by Forbes in 2008, with a fortune estimated at more than 50 billion dollars.