KABUL -- Two suicide bombings and a host of looming disagreements with the Afghan president cast a shadow Saturday over U.S. Defense Secretary Chuck Hagel's first visit to Afghanistan since taking the post.

Nineteen Afghans were killed -- including eight children -- in the suicide attacks in Kabul and in the eastern Khost province. A U.S. contractor was killed and four soldiers injured when attackers thought to be Afghan soldiers stormed their base and opened fire Friday, just hours before Hagel arrived.

"This attack was a message to him," Taliban spokesman Zabiullah Mujahid said in an email to reporters about one of the bombings, which was outside the country's Defense Ministry in Kabul.

Afghan President Hamid Karzai, meanwhile, was standing by a demand that U.S. special operations forces leave a province neighboring Kabul by Monday for alleged abuses of Afghan civilians -- charges U.S. officials deny. And a handover ceremony scheduled for Saturday of a U.S. detention facility fell through when U.S. and Afghan officials ran into last-minute disagreements.

The barrage of crises heralding Hagel's arrival illustrates the complex minefield of diplomatic and military issues facing the U.S.-led NATO force, and the Obama administration, as they hand over the country's security to Afghans ahead of the 2014 deadline for the end of NATO combat operations.

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The violence also shows the Afghan security forces' struggle to contain the Taliban as NATO troops slowly withdraw, even as Karzai argues for his government to have more control over Afghanistan's security.

Hagel told reporters he thought he could resolve the special operations issue with face-to-face meetings with Karzai Sunday. And Karzai released a statement late Saturday saying he thought the detention issue had been resolved, and the handover would go ahead within a week, though U.S. officials had no comment.