Russian President Vladimir Putin says he has no doubt that North Korea is serious about a bilateral treaty, which includes a promise of mutual military assistance if either country is attacked.

Putin made the remarks at a news conference on Thursday.

Members of Russia's lower house of parliament voted that day to accept the comprehensive strategic partnership treaty. Members of the upper house are expected to follow.

Putin signed the deal with North Korean leader Kim Jong Un during his visit to North Korea in June.

Article 4 stipulates that if either of them is invaded and placed under a state of war, the other will deploy all means in its possession to provide military and other assistance, without delay.

Putin commented on the bilateral military cooperation in an interview with a state-run TV station after Thursday's news conference, saying, "When we have to decide something, we will certainly decide." But he did not elaborate further.

Ukraine announced that some North Korean troops had already arrived in western Russia, raising concerns in the international community.