WPP, the world's largest advertising group by revenue, said like-for-like sales grew more than 6 per cent in the four months to end-April, buoyed by the United States and in line with its forecast for the year.

The firm, led by Martin Sorrell and headquartered in Dublin, said today its US revenue was up almost 8 per cent year to date and British sales grew by more than 7 per cent despite economic pressures, while continental Europe was up more than 3 per cent.

All advertising groups have been lifted in the last 12 months by a stronger than expected performance in the US market and WPP has also rebounded well from the downturn due to its strong position in key markets such as India and China.

Separately, WPP said it had bought a majority stake in Brazil's largest independent digital agency f.biz for an undisclosed price. F.biz has 200 staff and had revenue of $30.1 million reals ($18.9 million) last year.

WPP said tsunami-hit Japan was its only Asian market not to have grown and said the situation was unlikely to change for most of this year. Political turmoil in the Middle East was continuing to have an impact, with year to date revenue flat.

WPP, whose ad agencies include JWT and Ogilvy & Mather, said it would continue to focus on balancing headcount growth and sales growth, but would grasp market opportunities and invest in new or existing talent where necessary.

"We continue to be cautiously optimistic about the prospects for the remainder of 2011 and, indeed for 2012," Mr Sorrell said in a statement.

"2013 may be challenging, as a re-elected or new United States president has to finally wrestle with the colossal fiscal deficit."

In March, Mr Sorrell said the group was considered shifting its HQ back to the UK following changes to taxation proposed in the budget.