(For full coverage of Afghanistan, click on [nAFPAK])
* Attacks will not thwart election run-off - White House
* Senator Kerry calls for information on Karzai brother
* Clinton confirms one American among five dead foreigners (Adds lawmakers on Karzai's brother, updates death toll)
By Sue Pleming
WASHINGTON, Oct 28 The United States vowed on Wednesday it would not be intimidated after an attack on a U.N. guest house in Kabul, as the Obama administration dodged reports that Afghan President Hamid Karzai's brother was being paid by the CIA.
White House spokesman Robert Gibbs condemned the attack in which one American was among five U.N. staff killed, saying it was an attempt to disrupt Afghanistan's Nov. 7 presidential run-off election and "will not succeed."
"The administration is confident that there are the appropriate resources to conduct an election and that the will of the Afghan people won't be thwarted," Gibbs told reporters.
U.S. Secretary of State Hillary Clinton, on a visit to neighboring Pakistan where militants bombed a marketplace, strongly condemned the "cowardly" attack in Kabul.
"The United States remains steadfast in its support for the United Nations and its vital work to help the Afghan people," she said in a statement in which she confirmed one American working for the United Nations was killed.
The White House, in the midst of a review of Afghan war strategy, faced a barrage of questions after a report in The New York Times that Karzai's brother was getting regular payments from the Central Intelligence Agency.
There are divisions within the administration over how to handle Karzai, seen as failing to crack down on corruption. There have also been questions over his brother, Ahmed Wali Karzai, a suspected player in Afghanistan's opium trade.
The New York Times said Karzai's brother had been paid by the CIA for services that included helping to recruit an Afghan paramilitary force that operates at the CIA's direction in and around the southern city of Kandahar.
The White House deferred questions on the subject to the CIA, which neither confirmed nor denied the story.
But Gibbs repeated a U.S. demand that any Afghan government must "address governance issues" and said this had been raised at each meeting to discuss the review of strategy.
Leading lawmakers demanded answers from the Obama administration.
Democratic Senator John Kerry, who earlier this week defended Karzai and his brother, said senior U.S. officials had told him repeatedly there was no "hard evidence" about the allegations against the Afghan president's sibling.
"I have serious questions about the information that Congress is receiving. On questions this serious, it is imperative that we receive reliable, current and accurate information," Kerry said in a statement.
He said "critical" U.S. relations with Karzai should not be damaged on the basis of newspaper articles and rumors and neither should his brother be condemned.
"But the appropriate congressional committees must be immediately provided with the most comprehensive and untainted information about his alleged entanglements," he added.
MEETING ON FRIDAY
Republican Senator John McCain said he had heard a "rumor" of Karzai's brother being in the pay of the CIA, something U.S. military commanders would not agree with.
"Karzai's brother should not be in the country," McCain told CBS' morning television show.
The latest violence comes as President Barack Obama is closing in on a decision whether to send in at least 40,000 more troops, as recommended by General Stanley McChrystal, commander of U.S. and NATO forces in Afghanistan.
As part of that review, Obama will meet at the White House on Friday with Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, and with the heads of the military services.
Obama's advisers, having ruled out troop reductions, are discussing how many more combat and training brigades should be sent to Afghanistan next year, an administration official said.
Top officials appeared to be laying the ground for increasing troops with a focus on protecting population centers, combined with a stepped-up counterterrorism campaign in the countryside and along the Afghanistan-Pakistan border.
This strategy, the official said, would likely entail a troop increase, though not necessarily as large as 40,000. (Additional reporting by Steve Holland, Adam Entous and Phil Stewart; editing by Todd Eastham)