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North Korea may get pushier next year: Nomura

TV footage showing North Korean leader Kim Jong-Un attending a ceremony marking the third anniversary of late leader Kim Jong-Il's death on December 17, 2014.
JUNG YEON-JE | AFP | Getty Images
TV footage showing North Korean leader Kim Jong-Un attending a ceremony marking the third anniversary of late leader Kim Jong-Il's death on December 17, 2014.

Claims that North Korea has engaged in recent cyber-attacks could see the rogue nation ramp up military aggression next year, Nomura said.

Last week, the Federal Bureau of Investigation (FBI) announced that North Korea was behind a recent hacking at Sony Pictures, sparking expectations of U.S. retaliation against Pyongyang. Separately, following the FBI announcement, South Korea's nuclear plant operator announced a breach of its computer systems.

"Markets should be braced for a possibly protracted period, i.e. some weeks, of raised tensions around North Korea, which may trigger not only the usual rhetoric and missile launches by Pyongyang - as well as, possibly, the fourth nuclear test which has been threatened for some time now - but also potentially something (cyber or otherwise) more serious," said Alastair Newton, senior political analyst at Nomura, in a note on Wednesday.

The annual South Korea- U.S. military exercises, typically set for February or March, also usually raise tensions with the North, he noted. "It would be surprising if we were not to see this pattern repeated in 2015," he added.

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In February this year, South Korea's Defense Ministry reported that North Korea fired several short-range missiles into the sea just days after the U.S. and South Korea began their joint exercises. Meanwhile, March 2013 saw the isolated nation threaten the U.S. with a nuclear strike, accusing Washington of using military drills with South Korea as a pre-text for nuclear war.

"Furthermore, the anniversary of the birth of Kim Il-sung on 15 April is an occasion when Pyongyang traditionally likes to make a show of strength of some sort," Newton added.

This past April, Pyongyang pledged to restart a nuclear complex shut down in 2007 as well as threatening military aggression against both South Korea and the U.S.

North Korea's capital city experienced an Internet shutdown this week, fuelling speculation it was payback from Washington, but U.S. authorities have since denied involvement. If the U.S. does apply pressure on North Korea -- such as a repeat of 2013's strict economic sanctions -- Nomura believes inter-Korean relations could deteriorate further.

U.S. President Barack Obama has said his administration will make a "proportional" response to the Sony attack in a place, time and manner that America chooses.

Read MoreHow to hit back at North Korea for Sony cyberattack

Is it really that serious?

Some experts told CNBC they aren't entirely convinced of the gravity behind Sony's cyber breach.

"Which large company hasn't been hacked? Apple's Cloud was hacked before the iPhone 6 launch. The world doesn't stop there," said Atul Goyal, senior analyst at Jefferies, on Monday.

Others aren't even convinced that North Korea was the guilty party.

"It's possible that it was North Korea, but I haven't seen the evidence to prove it. Even if it was them, is this an act of war? You don't typically start a war by going after a company's movie - it would be the weirdest act of war in our lives. This could be a plot for another movie," said Mark Rasch, Founder of MarkDRasch.com and former head of the U.S. Justice Department's computer crime unit.