By Andrew Quinn

KABUL (Reuters) - Secretary of State Hillary Clinton will discuss possible peace talks and Afghanistan's tricky ties with Pakistan when she meets Afghan President Hamid Karzai and other key leaders in Kabul on Thursday, U.S. officials said.

Clinton's arrival on Wednesday on an unannounced visit to Afghanistan follows several high profile attacks in the Afghan capital, including an assault on the U.S. embassy in September and days later the assassination of Karzai's top peace envoy, former President Burhanuddin Rabbani.

"She wants to signal U.S. support for a secure and stable Afghanistan," a senior U.S. official told reporters traveling with Clinton.

"She wants to emphasize that the United States remains committed to Afghan reconciliation and will support President Karzai in his efforts, recognizing the difficulties that process has undergone since the assassination of Rabbani."

The visit comes as Afghanistan, Pakistan and the United States all see strains in their relations, complicating the outlook as the Obama administration pushes ahead with plans to draw down troops and turn over security responsibility to Afghan forces by the end of 2014.

Efforts to reach a political solution to a conflict now over a decade old will be on Clinton's agenda, along with support for Afghans as they step up their own security work, the official said.

Clinton will meet Karzai and other Afghan officials, U.S. officials said, and hold a round-table meeting with non-government leaders and civil society activists. She will also hold a joint news conference with the Afghan president.

U.S. officials said Clinton would also discuss the future "strategic partnership" between Afghanistan and the United States after 2014, with an eye to eventually formalizing the alliance.

"She'll want to point to that as a signal to Afghans, to the region, that the Untied States will remain committed to Afghanistan beyond 2014."

PAKISTAN AND THE REGION

Clinton is expected to preview plans for conferences on the future of Afghanistan due to be held in Istanbul in November and Bonn in December which U.S. officials hope will tighten international cooperation on political and economic strategies to stabilize the country.

She is also expected to discuss ties between Afghanistan and neighboring Pakistan, accused by officials in both Afghanistan and the United States with working to undercut the U.S.-led military campaign in order to protect its influence in the region.

Ties between Kabul and Islamabad have been particularly strained since the assassination of Rabbani, who was killed by a suicide bomber posing as a Taliban reconciliation envoy.

Many Afghans, including senior officials, have accused the Pakistan government of having links to the killing, and accused their neighbor of fomenting instability to further its own political interests. Pakistan denies this.

Karzai has been more circumspect, but hinted after the killing that he had lost hope in pursuing peace talks with the Taliban and suggested negotiations with Pakistan instead.

Top U.S. officials have also accused Pakistan of supporting insurgent groups in Afghanistan after September's 20-hour attack on diplomatic targets in Kabul, including the U.S. embassy.

But President Barack Obama and Clinton have both stressed that the U.S. relationship with Pakistan is too important to abandon, although Clinton said last week if Islamabad did not help solve Afghanistan's difficulties it would "continue to be part of the problem."

(Writing by Christine Kearney and Andrew Quinn, editing by Emma Graham-Harrison and Andrew Heavens)