European leaders on Tuesday put pressure on British Prime Minister David Cameron to expedite his country's exit from the European Union after its decision to leave rocked global markets.

Adding to the pressure, Standard & Poor's stripped Britain of its top-notch debt rating late on Monday following Thursday's referendum result.

Cameron, who had fought to remain in the EU and has said he will step down, told Parliament on Monday that he will not start the two-year countdown yet on leaving the bloc by invoking Article 50 of the Lisbon Treaty.