.

US senators scuffled Sunday over the US credit downgrade, with a top Democrat blaming the ultra-conservative Tea Party and a top Republican accusing the White House of failing to lead.

Standard & Poor's has said that one of the main reasons it downgraded the long-term US credit rating from a sterling AAA to AA+ was because of the political gridlock that has kept Washington from balancing its finances.

But on Sunday Senator John Kerry, a moderate Democrat, called the move a “Tea Party downgrade” and said a debt deal reached last week fell short because some Republicans “were willing to shoot the hostage.”

“What we need is a Washington that stops this bickering,” Kerry told NBC's Meet the Press.

The deal to cut some $2.5 trillion over 10 years - reached after weeks of tense negotiations - fell short of the S&P's call for the United States to cut $4 trillion of its bloated national debt.

Senator John McCain, a moderate Republican appearing on the same talk program, blamed US President Barack Obama, saying he had failed to put forth a specific plan for reining in debts and deficits.

“I agree that there is dysfunction in our system, but a lot of it has to do with the failure of the president to lead,” he said.

He went on to defend the Tea Party movement's rejection of any new tax revenues, saying they were acting on a mandate from voters who swept Republicans to a House of Representatives majority in elections last fall.

He then echoed Kerry's call for civility, saying: “Lately the Democrats have been calling us terrorists, so we need to lower that level of rhetoric.”

McCain also defended the S&P from allegations by the Obama administration that it erred in its research, saying: “Don't shoot the messenger.”

“Is there anybody that believes that S&P is wrong in their assessment of the fiscal situation of this country?”

In defending the first-ever decision to cut the US credit rating, S&P global head of sovereign ratings David Beers said Friday that the political paralysis in Washington was a major factor.

“I think it's safe to say that the nature of the debate and the difficulty in framing a political consensus about how to make fiscal policy choices were the key considerations,” he told reporters. - Sapa-AFP