By Tabassum Zakaria and Mark Hosenball
(Reuters) - The United States is preparing to accede to Pakistani demands that it vacate a remote air base in Pakistan used for drone flights, but the move is not expected to have a significant impact on operations against militants, U.S. government sources say.
Washington is treading lightly not to aggravate an already fragile relationship that was bruised further by a NATO attack on a Pakistani military outpost last weekend that killed 24 Pakistani soldiers near the Afghanistan border.
Pakistan demanded that the United States leave the Shamsi Air Base within 15 days and blocked ground supply routes through Pakistan to U.S. forces in Afghanistan.
Three sources, who declined to be identified because of the issue's sensitivity, said U.S. planning is under way to leave the base, a remote facility in Baluchistan that has been a point of contention.
The cross-border incident escalated tensions between the two countries and the U.S. military is conducting an investigation to find out exactly what happened on the ground.
The moves by the Pakistanis to block ground supply routes and the air base were not expected to significantly hinder U.S. operations.
One U.S. government source said the United States has spent months preparing for a possible eviction from the Pakistan base by building up other drone launching and staging capability.
Earlier this year, after the U.S. raid that killed al Qaeda leader Osama bin Laden, some Pakistani officials demanded that Washington vacate the Shamsi facility.
At the time, however, U.S. officials said that American personnel would remain at the base and would continue to conduct drone flights in pursuit of militants.
But in one concession, the United States stopped conducting lethal drone operations from that base and limited operations to surveillance flights.
U.S. officials believe that this time Pakistan appears much more resolute about carrying out the eviction threat. Vacating the air base was seen more as an inconvenience rather than a critical blow to drone operations which the United States also conducts from Afghanistan and possibly elsewhere.
The unmanned aerial vehicles may have a longer flight from Afghanistan but they are capable of hovering overhead for hours as they seek to spot suspicious activity and follow militants.
U.S. officials are reluctant to openly talk about drone operations because they are considered a covert CIA activity.
General Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff, in London this week addressed the Shamsi issue without acknowledging the use of drones at the base.
"There are other options for stationing aircraft and other resources around the region," Dempsey told Britain's ITV News.
"It's a serious blow in the sense that the Pakistani government felt that they needed to deny us the use of a base that we've been using for many years," he said. "And so it's serious in that regard. It's not debilitating militarily."
BLOCKED SUPPLY ROUTE
The United States also has to deal with the blocking of the ground supply route through Pakistan to Afghanistan.
Congressman C.A. "Dutch" Ruppersberger, the senior Democrat on the House of Representatives intelligence committee, said that route accounts for less than half the supplies for international forces in Afghanistan and the military has contingency plans.
"We have a large distribution network to make sure that coalition forces are well-stocked," he told Reuters. "It's not going to affect our ability to follow through and execute our mission."
Yet alternate supply routes such as the northern distribution network are not a perfect substitute and there are concerns that the cost of keeping soldiers fed, armed and fueled without use of Pakistani roads would be excessive.
Ruppersberger, who visited Pakistan to meet with officials after U.S. forces killed bin Laden, said the relationship was poor at that point.
"We were starting to improve in the last month or so and then all of a sudden this unfortunate incident occurred, and now we're right back to where we were again," he said.
"It is to the advantage of both countries to work together," Ruppersberger said. "In the end that will come. It's about relationships, it's about trust, and unfortunately that hasn't been there for a while."
Ruppersberger would not comment on the Shamsi departure.
U.S. officials said there is still considerable confusion about details of the latest border incident.
Wary of further damaging an already delicate situation, U.S. officials were reluctant to speculate about what happened before getting the results of military investigations.
"The focus of the administration at this point is on trying to find ways to show Pakistan that we're serious about investigating the incident and forging a cooperative relationship in the future," a U.S. official said on condition of anonymity.
"No one at this point has the complete narrative on what happened," Pentagon spokesman George Little said. "I think it's premature to articulate the facts of this incident."
A U.S. government source familiar with counter-terrorism operations along the Afghan-Pakistan border said the latest incident apparently grew out of an Afghan-U.S. special forces commando patrol operation.
Some early information from the region suggests that at some point the Afghan-U.S. patrol team came under fire from what they believed were militants. They then called in an airstrike, which hit a Pakistani military outpost.
Investigations into the incident now are trying to determine if the militants deliberately took up positions near the Pakistani outpost to confuse American and Afghan forces or whether Pakistani forces at the border outpost were somehow complicit in initially firing on the Afghan-U.S. patrol.
A U.S. military official, without commenting on details of the current incident, said the Taliban had previously tried to provoke cross-border fighting between Pakistani soldiers and NATO forces but problems were headed off by cross-border communication.
"It is something we've seen previously, yes. I wouldn't be surprised if something like that happened," the official said, without confirming anything about the recent incident.
Another key question is what happened to cross-border communication systems set up to avoid this kind of confusion.
The border between Afghanistan and Pakistan is badly marked, and disputed in many stretches. The terrain of steep mountains, dense forest and sparse population provides hideouts for militants who can move freely along the frontier.
The Pakistani and Afghan militaries and NATO-led alliance have tried to limit deadly mistakes by establishing communication links including a hotline to check on potential targets or warn of possible friendly fire.
The Pakistani military says it has given maps with permanent outposts clearly marked to NATO and the Afghan army. It also said there is a hotline between the two sides, but declined to say if it was used the evening of the attack.
A spokesman for the NATO-led International Security Assistance Force said he was not aware of a hotline.
(Additional reporting by Missy Ryan, Phil Stewart, Emma Graham-Harrison; Writing by Tabassum Zakaria in Washington; Editing by Deborah Charles and Cynthia Osterman)