ROME (Reuters) - Russian Foreign Minister Sergei Lavrov said on Friday that a U.S. threat to destroy North Korea in the event of a war was "a bloodthirsty tirade" and military action against Pyongyang would be a big mistake.

Speaking on a visit to Italy, Lavrov strongly condemned comments made by U.S. Ambassador to the United Nations Nikki Haley, who earlier this week warned North Korea's leadership it would be "utterly destroyed" if war were to break out after Pyongyang test fired its most advanced missile.

"If someone really wants to use force to, as the U.S. representative to the United Nations put it, destroy North Korea ...then I think that is playing with fire and a big mistake," Lavrov told reporters.

He called Haley's speech on North Korea, which she made at an emergency U.N. Security Council meeting, "a really bloodthirsty tirade".

"We will do everything to ensure that (the use of force) doesn't happen so that the problem is decided only using peaceful and political-diplomatic means," said Lavrov.

Later, addressing a Rome conference, Lavrov said Russia and the United States both wanted North Korea to disarm, but said Washington would send a bad message if it walked away from a 2015 nuclear deal with Iran.

U.S. President Donald Trump said in October he would not certify that Tehran was complying with the 2015 deal and warned he might ultimately terminate it, accusing Iran of "not living up to the spirit" of the accord.

"If the United States drops out of this deal, it won't be very credible in the eyes of those who are now requested to drop their (own) nuclear program like North Korea," Lavrov said.

He added that most "serious analysts ... and many officials" in Washington understood this.

(Reporting by Andrew Osborn and Dmitry Solovyov in Moscow and Crispian Balmer in Rome; Editing by Matthew Mpoke Bigg)