(CNN)-- President Barack Obama made a previously unannounced visit to Afghanistan on Tuesday, the first anniversary of the U.S. raid that killed Osama bin Laden in neighboring Pakistan.
On his third trip to Afghanistan since taking office, Obama will meet with Afghanistan President Hamid Karzai and make a televised address from Afghanistan at 7:30 p.m. ET.
Tuesday's visit comes at a particularly delicate time in relations between the United States and Afghanistan. The countries have been negotiating a strategic agreement that would outline the basis for U.S.-Afghan cooperation after most U.S. and allied troops withdraw in 2014.
Obama and Karzai are expected to sign the agreement on Tuesday.
More than 130,000 troops from 50 countries serve in Afghanistan, according to the NATO-led International Security and Assistance Force. The United States is the biggest contributor, providing around 90,000 troops, followed by the United Kingdom (9,500), Germany (4,800) and France (3,600).
The war that began in 2001 is increasingly unpopular in the United States, with the latest CNN/ORC International poll in late March showing 25% of respondents supporting it while 72% opposed it.
More than 2,700 troops from the United States and its partners have died in the war, the majority of them American.
In 2011, the United States outlined its plan to withdraw its troops from Afghanistan by the end of 2014. The move was followed by withdrawal announcements by most of the NATO nations.
Last week, Afghan National Security Adviser Rangin Daftar Spanta and U.S. Ambassador Ryan Crocker initialed a text that outlined the kind of relationship the two countries want in the decade following the NATO withdrawal.
The deal had been long expected after Washington and Kabul found compromises over the thorny issues of "night raids" by U.S. forces on Afghan homes and the transfer of U.S. detainees to Afghan custody.
Obama previously visited Afghanistan in March 2010 and returned in December of the same year. He also visited Afghanistan in 2008 as a presidential candidate.
A new report issued Tuesday by the Pentagon said that sanctuaries for insurgents in neighboring Pakistan continue to be a problem for the coalition forces and Afghan government.
"The Taliban-led insurgency and its al Qaeda affiliates still operate with impunity from sanctuaries in Pakistan," the semi-annual report said, adding that "the insurgency's safe haven in Pakistan, as well as the limited capacity of the Afghan government, remain the biggest risks to the process of turning security gains into a durable and sustainable Afghanistan."
While the coalition is on track to turn security fully over to Afghan control, the insurgency "remains a resilient and determined enemy and will likely attempt to regain lost ground and influence this spring and summer through assassinations, intimidation, high-profile attacks and emplacement of improvised explosive devices," according to the report.
The report covers security developments in Afghanistan from October through March. It noted several "significant shocks" during that period, including release of a video of U.S. Marines urinating on corpses, the inadvertent burning of religious materials by U.S. personnel, several "green on blue" incidents in which coalition forces were killed or wounded by Afghan troops, and the alleged killing of 17 civilians by a lone U.S. soldier.
However, the report also noted that the insurgency has been "severely degraded" by Afghan and NATO combat operations, noting the "most significant security-related development" during the reporting period was the continuing decline in violence.
After five consecutive years in which enemy attacks had increased, they decreased by 9% in 2011 and by 16% so far in 2012.
The report attributed the improvement to the expansion and improved training of Afghan security forces. Afghans partner with coalition forces on 90% of coalition operations, taking the lead on about 40% of them, according to the military.
Along with the insurgent sanctuaries in Pakistan, the report noted that Iran is trying to ensure a "dominant, long-term role" for itself in Afghanistan along with the permanent withdrawal of foreign forces.
While much of Iran's activity involves openly reaching out with economic and cultural support, the report said there also is "covert support, including the provision of weapons and training for various insurgent and political opposition groups," including the Taliban.