By Andrew Quinn

ISLAMABAD (Reuters) - Secretary of State Hillary Clinton said Friday that the United States had held a preliminary meeting with representatives of the Haqqani network, a group of militants Washington has blamed for a series of attacks in Afghanistan.

Clinton was in Islamabad to discuss joint efforts against militants, and was asked at a journalist roundtable about reports that U.S. officials had met with Haqqani representatives directly, even as Washington demanded that Pakistan take a tougher line on the group.

"We have reached out to the Taliban, we have reached out to the Haqqani network to test their willingness and their sincerity, and we are now working among us -- Afghanistan, Pakistan and the United States -- to try to put together a process that would sequence us toward an actual negotiation," Clinton said.

No negotiations are underway, she said.

A senior U.S. official said later that the meeting took place in the summer, before September's attack on the U.S. embassy in Kabul that U.S. officials have linked to the Haqqanis.

They said the meeting had been organized by Pakistan's powerful spy agency, the Directorate of Inter-Services Intelligence (ISI), which U.S. officials have repeatedly charged with playing a "double game" with Islamist extremists and working with the Haqqanis.

"Pakistani government officials helped to facilitate such a meeting," Clinton said.

The U.S. Treasury last month imposed sanctions on individuals it said were linked to the Haqqani network, but stopped short of putting the group on the official U.S. blacklist of terrorist groups, which would bar any official contact.

"We had one preliminary meeting to essentially just see if they would show up for even a preliminary meeting," Clinton said.

The U.S. official described the Haqqani meeting as one of a number of "straws in the wind" that the United States is pursuing as it seeks to set the framework for an eventual political settlement in Afghanistan.

(Editing by Chris Allbritton and Paul Tait)