Barack Obama has blamed the 'kitchen-sink strategy' of rival Hillary Clinton for his defeat as his campaign pledged to strike back in the grinding Democratic United Stated presidential race.

After winning three of the four states in the Tuesday contests, including the crucial Ohio and Texas, Clinton looked all set to fight until the national convention in August. The Obama camp pointed out that she still lags behind in the delegate count as also the number of states won.

Obama, maintaining a 1,567-1,462 lead, said he remains well positioned in the battle for delegates.

"The delegate count is essentially unchanged from where it was yesterday," he said. "And, so now we go to Wyoming and Mississippi. We think we'll do well this week."
 
The Illinois Senator, vying to be the first back President of the United States, blamed the very negative campaign by his rival for the unexpected defeats on Tuesday.

"There's no doubt that Senator Clinton went very negative over the last week," he said. "And the kitchen-sink strategy, I'm sure, had some impact, particularly in a context where many of you in the press corps had been persuaded that you had been too hard on her and too soft on me," he said.

The Clinton camp took an aggressive approach in the recent days, questioning Obama's sincerity in opposing the North American free trade treaty, his links with a disgraced fundraiser and running a television ad that hints Obama is not experienced enough to trust during a national security crisis.

Obama's campaign started to sharpen its attacks on Wednesday, distributing a memo to ask why Clinton has not released her tax return. Her campaign said the Clintons' returns since they left the White House will be made public around April 15.

Obama also asked the media to more thoroughly examine Clinton's claims on foreign policy experience.

"One of the things, you know, I hope people start asking is what exactly is this foreign experience that she's claiming," Obama said.

"She talks about visiting 80 countries," he said. "It's not clear, you know, was she negotiating treaties or agreements or was she handling crisis during this period of time. My sense is the answer is no. I have not seen any evidence that she is better equipped to handle a crisis."

Meanwhile, some Democrat leaders have started worrying that the bitter rivalry between the two party contenders may actually help the Republicans during the November presidential polls.

New Mexico Governor Bill Richardson, who was once in the nomination race before pulling out, warned in a television interview, "The negativity between the two Democrat rivals could be campaign fodder for Republicans in the fall."