By Saud Mehsud

DERA ISMAIL KHAN, Pakistan (Reuters) - A suspected U.S. drone strike killed a close aide of the commander of the Haqqani militant group in Pakistan's North Waziristan region on the Afghan border Thursday, intelligence officials said.

The strike came as U.S. special representative Marc Grossman arrived in Islamabad to meet top officials and mend ties strained by recent U.S. allegations that Pakistan is supporting the Haqqanis, blamed for high-profile violence in Afghanistan.

Jalil Haqqani, 33, who helped organize the Haqqanis' operations and coordinate the group's affairs, was one of four militants killed when two missiles allegedly fired by a U.S. drone struck a house in the village of Dande Darpa Khel.

"Jalil was a highly trusted companion of Sirajuddin. He had been with the Haqqani group for a long time and was tasked with handling communications," one intelligence official said, requesting anonymity.

The Haqqanis, led by Sirajuddin Haqqani, have emerged as a major source of tension in U.S.-Pakistani ties, with former chairman of the Joint Chiefs of Staff Admiral Mike Mullen calling them a "veritable arm" of Pakistan's spy agency, the Directorate of Inter-Services Intelligence (ISI.)

Pakistani officials have angrily denied U.S. allegations that it is helping militant groups like the Haqqani network strike at NATO and Afghan targets in Afghanistan, including a September 13 attack on the American embassy in Kabul.

"We have never paid a penny or provided even a single bullet to the Haqqani network," ISI chief Lieutenant-General Ahmed Shuja Pasha told Reuters recently.

The Haqqanis are believed to be based in Pakistan's North Waziristan tribal area, but in a recent interview with Reuters, Sirajuddin said his group felt secure enough to operate freely in Afghanistan and had no need of safe havens in Pakistan.

U.S. Secretary of State Hillary Clinton told Reuters on Tuesday that the United States remains open to a peace deal including the Haqqanis, despite their alleged involvement in attacks in Afghanistan, including a September 13 attack on the American embassy in Kabul.

"We are not shutting the door on trying to determine whether there is some path forward," Clinton told Reuters when asked whether she believed members of the Haqqani network might reconcile with the U.S.-backed Afghan government.

Sirajuddin told Reuters in September that his group would take part in peace talks, but only if the Afghan Taliban did so as well, a shift from his earlier position.

He has previously rejected several peace gestures from the United States and President Hamid Karzai's government, calling them an attempt to "create divisions" between militant groups.

Grossman, appointed in February, held meetings with Pakistan's prime minister, the chief of the country's powerful army and the foreign minister, according to Pakistani state television.

His visit comes at a time of some of the worst tensions in U.S.-Pakistani ties, already badly strained after a May 2 commando raid killed al Qaeda leader Osama bin Laden, who had apparently been living in a garrison town near Islamabad for nearly five years.

The United States did not tell Pakistani of the raid in advance because of concerns bin Laden might have been tipped off by possibly sympathetic elements in the ISI.

Pakistan reacted angrily to the raid, denouncing it as a breach of sovereignty and a display of mistrust between allies.

Clinton said Wednesday the United States had no choice but to work with Pakistan in trying to stabilize neighboring Afghanistan.

"As frustrating as it is, we just keep every day going at it and I think we make slow, sometimes barely discernible progress," she said at an event sponsored by the Center for American Progress in Washington, while answering questions.

"But we're moving in the right direction."

(Writing by Qasim Nauman; Editing by Chris Allbritton and Raju Gopalakrishnan)