With that timetable on track, Crocker’s departure from Kabul will not likely herald any new U.S. approach to the conflict. However, the loss of his presence as a trouble-shooter since the 1980s will be felt as the administration struggles to prevent Afghanistan from descending again into the cauldron of extremism that gave sanctuary to Osama bin Laden and leaders of his al-Qaida network.

The U.S. embassy in Kabul confirmed Crocker’s departure “with regret” while officials in Washington said he made his plans known to Obama during this weekend’s NATO summit in Chicago at which the allies discussed the way forward in Afghanistan.

In Afghanistan for his second tour as America’s top U.S. envoy in Kabul — he reopened the U.S. embassy there in 2002 after the ouster of the Taliban regime — Crocker was called on to lead a ramp-up in civilian operations similar to one he supervised in Iraq.

In nominating Crocker for the Kabul post, Obama hailed him as “one of our nation’s most respected diplomats,” who “is no stranger to tough assignments.”

Indeed, Crocker was a six-time ambassador, running embassies not only in Iraq and Afghanistan but also in Pakistan, Kuwait, Lebanon and Syria. An Arabic speaker, he held diplomatic posts in Qatar, Iran, Egypt and Lebanon earlier in his career.

As a young officer, he was in Beirut when the U.S. Embassy there was blown up in 1983. His residence in Syria was ransacked by a mob when he was ambassador there in 1998.

Such experiences contributed to Crocker’s calm under fire. When a Pakistan-based group allied with the Taliban staged a spectacular attack on the U.S. embassy in Kabul last September — taking over a nearby building and firing rockets and bullets at the compound during a 20-hour siege — Crocker was unfazed.

“This really is not a very big deal,” he told reporters at the time. “If that’s the best they can do, you know, I think it’s actually a statement of their weakness.”

It is not immediately clear who will replace him, although officials said the most likely candidate is James Cunningham, a former ambassador to Israel and deputy U.N. envoy who is now one of the ex-ambassadors serving under Crocker in Kabul.

Crocker will leave his post in mid-summer, after international donor conferences for Afghanistan are held in Tokyo and Kabul, State Department spokeswoman Victoria Nuland said in a statement.

“Ambassador Crocker’s tenure has been marked by enormous achievements,” she said, listing the successful negotiation of a strategic partnership agreement with Afghanistan and the Chicago summit as highlights.

Perhaps one of the best known ambassadors outside the famously insular diplomatic circuit because of his 2007-2009 stint as U.S. ambassador to Iraq during former President George W. Bush’s military “surge” — a period in which he testified before Congress in nationally televised hearings with his military counterpart Gen. David Petraeus — Crocker was favored by Republicans and Democrats alike to correct errant policies, clean up messes and begin planning for the drawdown of U.S. forces.

Crocker ran the civilian side of Bush’s buildup, overseeing a massive influx of development experts, diplomats and academics throughout the country as it emerged from a brutal and relentless insurgency and fought to improve infrastructure, governance and the rule of law. He and Petraeus laid the groundwork for the eventual withdrawal from Iraq.

After leaving public service following his time in Baghdad, Crocker became dean of Texas A&M University’s George Bush School of Government and Public Service. But he was pressed back into duty in Kabul in July 2011 to replace Ambassador Karl Eikenberry, a retired general whose poisonous relationship with Afghan President Hamid Karzai had become untenable.

Sen. John McCain, one of the top Republicans on the Armed Services Committee, told reporters, “Ryan Crocker has served the nation with such distinction and such a long time. I respect his decisions whatever they may be. Obviously I’d like him to stay forever. But he has other understandable priorities.”

_

Associated Press Writer Donna Cassata in Washington and Robert Reid in Cairo contributed to this report.

“Bahrain is an important security partner and ally in a region facing enormous challenges,” State Department spokeswoman Victoria Nuland said in a statement. Maintaining the ability to respond to such challenges is a critical part of the U.S. commitment to Gulf security, she said.

She said the administration is “mindful” of “serious unresolved human rights issues,” and that holds imposed on the transfer of some items, such as TOW anti-tank missiles and Humvees, would continue.

She stressed that items being released are not used for crowd control and that the U.S. remains concerned about excessive use of force and tear gas against opposition activists.

The announcement followed meetings in Washington this week between Vice President Joe Biden and Secretary of State Hillary Rodham Clinton and Bahrain Crown Prince Sheikh Salman bin Hamad bin Isa Al-Khalifa.

But it also came as Bahraini riot police on Friday fired tear gas and stun grenades during clashes with anti-government protesters following a rally calling for the release of detained activists, according to witnesses.

At least 50 people have died amid Bahrain’s unrest since it began in February 2011.

Nuland praised Bahrain’s government for taking “some important steps” to follow through on recommendations made by a special commission created to look into the violence.

But she added that much more work must be done to ease increasing polarization between majority Shiites and the ruling Sunni monarchy. And she lamented that some protestors were resorting to violence.

“We urge all sides to work together to end the violence and refrain from incitement of any kind, including attacks on peaceful protestors or on the Bahraini police,” Nuland said.