The United States is gearing up for what may be the last major American-run offensive of the Afghanistan war — a bid to secure the approaches to Kabul.

The U.S.-led spring offensive, expected to begin in the coming weeks, may be NATO's last chance to shore up Kabul's defenses before a significant withdrawal of combat troops limits its options.

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The focus will be regions that control the main access routes, roads and highways into the ancient city from the desert south and the mountainous east. These routes are used not only by traders carrying goods from Pakistan and Iran but also by militants, including the Taliban.

The Taliban made their intentions clear over the weekend, mounting spectacular coordinated attacks that spawned an 18-hour battle with Afghan and NATO forces.

While bombings and shootings elsewhere in Afghanistan receive relatively little attention, attacks in the capital alarm the general population, undermine the government's reputation and frighten foreigners into fleeing the country.

Kabul fighting ends after 18 hours of intense gunfire

That's why insurgents on Sunday struck locations that were so fortified they could cause little or no damage, including the diplomatic quarter, the parliament and a NATO base.

"These are isolated attacks that are done for symbolic purposes, and they have not regained any territory," U.S. Defense Secretary Leon Panetta said Monday.

The strategy in eastern Afghanistan involves clearing militants from provinces such as Ghazni, just south of the capital. The pivotal region links Kabul with the Taliban homeland in the south and provinces bordering Pakistan to the east.

NATO, under U.S. command, will also conduct more operations in eastern provinces such as Paktika and Paktia that are considered major infiltration routes to the capital from insurgent safe havens in Pakistan.

Afghan President Karzai slams NATO over 18-hour Kabul gunbattle

Afghan and U.S. officials blamed the Pakistan-based Haqqani network, which is part of the Taliban and has close links with al-Qaida, for the weekend attacks that left 36 insurgents, eight policemen and three civilians dead in Kabul and three eastern provinces.

But Army Gen. Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, said officials have not concluded whether the attacks emanated out of Pakistan.

Declining numbers of international troops in the coming months are also forcing coalition forces to focus less on remote and thickly populated places such as eastern Nuristan. They hope to move responsibility for those areas to the Afghan security forces.

Coalition forces last summer made gains in traditional Taliban strongholds such as Kandahar and Helmand provinces in the south, areas they must now hold with fewer troops.

By September, as many as 10,000 U.S. Marines are scheduled to leave Helmand and hand over the lead for security to Afghan forces in the former Taliban stronghold.

"It's going to be a very busy summer," Gen. John Allen, the top U.S. and NATO commander, said recently. "The campaign will balance the drawdown of the surged forces with the consolidation of our holdings in the south, continued combat operations" and an effort to push Afghan security forces into the lead.

The Afghan army and police are now in charge of security for areas home to half the nation's population, with coalition forces in a support role. The coalition hopes to keep handing over control until Afghan forces are fully in charge by the end of 2013, with all combat troops scheduled to withdraw from the country by the end of 2014.

The U.S. may retain a small number of forces past that date to help train and mentor the Afghan army and help with counterterrorism efforts.

There is very little appetite in Western countries for keeping troops in Afghanistan, but U.S. Ambassador Ryan Crocker said Sunday's attack shows the danger of withdrawing international forces too quickly.

"There's a very dangerous enemy out there with capabilities and with safe havens in Pakistan. To get out before the Afghans have a full grip on security, which is a couple of years out, would be to invite the Taliban, Haqqani, and al-Qaida back in and set the stage for another 9/11," Crocker said.

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