Boris Johnson has attacked the prime minister for achieving "two thirds of diddly squat" in his pre-referendum negotiations with Brussels.
The London Mayor hit back at his critics for "crowing too soon" in his Daily Telegraph column.
On his visit to the UK, Obama said being part of the European Union "enhances Britain's global leadership".
So I gather they think it's game over. The Bremainers think they have bombed us into submission.
They think that we have just seen the turning point in the referendum campaign, and that the British people are so intimidated by these testimonials - American presidents, business leaders, fat cats of every description - that they now believe the British people will file meekly to the polls in two months time and consent to stay in the EU; and thereby to the slow and insidious erosion of democracy in this country.
If that is indeed the view of the Remain campaign, they are crowing too soon.
Boris Johnson was heckled in Newcastle as he attacked David Cameron for "shamefully" spending £9.3 million of taxpayers' money on a pro-EU leaflet.
The London mayor criticised the "scared" tactics of the remain campaign as he continued his northern "Brexit blitz" tour.
But Boris had the start of his speech interrupted, with hecklers shouting "no Tories in Newcastle".
A group of women were escorted from the building.
Boris Johnson, who announced he is backing the Vote Leave campaign in the EU referendum, is making a speech on the first day of campaigning in Manchester.
Watch his speech live at the Old Granada Studios, Manchester:
- The live broadcast has now ended.
It has been a day of revelations, with some of the UK's most high-profile politicians offering the public a glimpse into their tax affairs.
Chancellor George Osborne released his figures from last year, showing that he earned a taxable income of £198,738 and paid £72,210 in tax.
London Mayor Boris Johnson published four years of records, revealing a total taxable income of £612,583. He paid £260,621 in tax.
Labour leader Jeremy Corbyn revealed that he earned a total taxable income of £72,645 and earned an extra £1,850 from other income sources. He paid £18,912 in tax.
ITV News' Julie Etchingham reports:
Boris Johnson claims US comments on Brexit debate are ironic given how fiercely the nation defends its own sovereignty.Read the full story ›
The London mayor told ITV News the email was 'a cockup' and that staff would be able to campaign as they saw fit.Read the full story ›
Boris Johnson's staff have been told to either back his stance on the EU referendum or remain tight-lipped, according to reportsRead the full story ›
London's mayor has told ITV News the June 23 referendum on EU membership is Britain's "chance to escape an oppressive structure".Read the full story ›
Boris claims if Britain votes to leave the EU "all options are good" as he believes the country will be able to strike new free trade deals.Read the full story ›
Francois Hollande has hinted France could scrap the current deal which stops thousands of migrants in Calais from entering the UK if Britain votes to leave the EU.
The French president warned of "consequences" from a Brexit as he hosted David Cameron at a Franco-British summit in the city of Amiens.
But Brexit campaigner Boris Johnson responded with a little schoolboy French to accuse the French government of scaremongering.
ITV News Deputy Political Editor Chris Ship reports from Amiens.