“Nothing could be further from the truth,” Brennan said.
The director of national intelligence said an “anticipatory warning” was given.
Russian troops reportedly launched an attack in Crimean port city of Sevastopol.
A NATO airstrike killed five Afghan soldiers on Thursday in a deadly friendly-fire incident.
Hagel said Wednesday that the U.S. military was acting in response to the crisis in Ukraine.
President Obama on Monday warned Russia that it faced economic and diplomatic isolation for its military intervention in Crimea.
A Ukrainian official said Russian troops have threatened to storm and seize the vessels.
Al Qaeda’s leader in Afghanistan is plotting a comeback once U.S. and NATO troops leave the country.
The officials insisted the mission that left 30 troops dead was not compromised.
The action by armed men comes as Russian troops are ordered to Ukraine's border.