Section 806 of the Patriot Act amends U.S. forfeiture law to allow authorities to seize all foreign and domestic assets from any group or individual that is caught planning to commit acts of terrorism against the U.S. or U.S. citizens. You can read more about that in a watered down version, here: [link]
Countries harboring or aiding terrorists are often subject to sanctions. Iran's one of them, as an example. So yeah, the government here can do this stuff.
A few years ago, Ross' mindset was not knowing where Thor and Hulk were was like losing track of nuclear weapons. And knowing how our government can get with anything coming from outer space? They'd be happy to let Loki end up in undisclosed limbo after a little gloating to make themselves look good. He's not a citizen of Earth, so that's makes it difficult for laws to protect him. Or Thor. Best a legal team can start with is take statements to clear Thor's name, and Jane can appeal the decision against her.
This would've been easy if a certain cranky ass magician decided to open a portal to Thor's brother.
Guessing from the silence on his end, that his answer is still a big fat NO.