THE HAGUE (REUTERS) - US President Barack Obama on Tuesday called Russia a "regional power" and said it had become involved in Ukraine out of weakness, not strength.

"Russia is a regional power that is threatening some of its immediate neighbours, not out of strength but out of weakness,"Mr Obama said after a nuclear security summit in the Netherlands.

"We (the US) have considerable influence on our neighbours. We generally don't need to invade them in order to have a strong cooperative relationship with them," he said.

He added that Russia is not the number one US national security threat and that he is more concerned about the possibility of a nuclear weapon going off in Manhattan.