Question

He claimed responsibility for the raid and showed off the weapons he says were seized from the Ukrainian army.

Answer 1

1. If you say that someone claims responsibility or credit for something, you mean they say that they are responsible for it, but you are not sure whether or not they are telling the truth.

http://dictionary.reverso.net/english-cobuild/claim%20responsibility​ 

2. to assert to be rightfully one's own <claimed responsibility for the attack>

http://www.merriam-webster.com/dictionary/claim​

او مسئولیت این حمله را پذیرفت/بر عهده گرفت و تسلیحات به دست آمده/ضبط شده از ارتش اوکراین را نشان داد.