WASHINGTON - US Republican presumptive presidential nominee Mitt Romney's campaign announced on Tuesday it had raised $7.4 million online in three days after the formal announcement of Congressman Paul Ryan joining the ticket.

Republican vice presidential candidate Paul Ryan speaks at a campaign stop at Lakewood High School in Lakewood, Colorado, Aug 14, 2012. [Photo/Agencies]

Paul Ryan, the 42-year-old Wisconsin lawmaker, has appeared to be a fund-raising powerhouse on a whirlwind campaign tour, shortly after he stood first time as Romney's vice-presidential running mate last Sunday. Romney's campaign raised 7.4 million dollars via more than 101,000 donations in 72 hours following the announcement, said Romney spokeswoman Andrea Saul on Tuesday.

Romney's choice of his running mate has dominated US media coverage with headline news and prime hour coverage ever since the announcement and effectively driven donations.

However, the amount fell shortly behind the Republican Party's record four years ago. In 2008, Republican presidential candidate John McCain campaign netted 8.8 million dollars in 48 hours after he announced Alaska Governor Sarah Palin as his running mate, the first female VP pick in Republican Party's history.

In July, Romney outraised Obama for the third straight month and raised over 100 million dollars for second straight month.

The Romney campaign also announced on Tuesday that it would not allow press to cover Paul Ryan's meeting with influential conservative political donor Sheldon Adelson in Nevada, despite regularly allowing press to cover fund-raising events. It also blocked media coverage of two Denver-area fundraisers on Monday with Ryan in attendance.

After stops in Virginia, North Carolina, Wisconsin, Iowa and Colorado earlier this week, Ryan will continue his campaign trial from Nevada to Ohio and Florida in the coming days.