Here we go:

From AFP:

Russia has sent "several hundred" troops into Ukraine's Crimea region, US defense officials said Friday, after Kiev called on Moscow to withdraw its forces from the peninsula.

"It looks like they’ve moved several hundred troops there (into Crimea)," a senior defense official, who spoke on condition of anonymity, told AFP.

The comments marked the first confirmation from President Barack Obama's administration that Russia had launched an incursion into Crimea.

The Russians had not given the US government advance notice of the action or explained its intentions since the operation was launched, officials said.

But Pentagon officials stressed Washington was focused on diplomacy, and there was no serious consideration being given to any US military action.

"It is now in the realm of diplomacy," said a second defense official, who asked not to be named.

Officials also said they were not aware of any request from Ukraine for military assistance.