WASHINGTON - Less than four months until the US presidential election, Republican candidate Mitt Romney's campaign is beefing up on personnel and investing more cash internally as outside groups pour millions into television ads to help him counter Democratic President Barack Obama's messaging over the airwaves.

Obama's spending still dwarfs Romney's June outlays , with two-thirds of it going toward advertising, but federal disclosures filed on Friday show the Republican candidate investing more in his campaign's infrastructure, something Obama did months ago, as the race has been stuck in dead heat.

Obama's campaign doled out $58.1 million in June, nearly twice as much as he raised, Friday's filings showed. Facing no competition within his own party, Obama got an early start on ad buys, framing his Republican challenger negatively.

Romney's campaign spent $27.5 million in June, nearly double the $15.6 million it spent in May and $12.6 million spent in April, when Romney first emerged as the presumed Republican presidential nominee.

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