North Korea fired an "unidentified projectile" early Thursday, Seoul said, its sixth apparent weapons test this year as the nuclear-armed country flexes its military muscles and ignores Washington's offers of talks.

The last time North Korea tested this many weapons in a month was in 2019, after high-profile negotiations between leader Kim Jong Un and then-United States president Donald Trump collapsed.

Since then, talks with the US have languished, and the country is reeling economically from biting international sanctions and a self-imposed coronavirus blockade.

"North Korea fired an unidentified projectile into the East Sea," Seoul's Joint Chiefs of Staff said, referring to the Sea of Japan.

Pyongyang fired two suspected cruise missiles on Tuesday, which are not banned under current UN sanctions on North Korea.

It also tested suspected ballistic missiles on January 14 and 17, and fired what it said were hypersonic missiles on January 5 and 11. 

The string of sanction-busting tests drew global condemnation, including a closed-door meeting of the UN Security Council meeting.

The United States also imposed new sanctions in response, prompting an angry reply from North Korea, which last week hinted that it could resume nuclear and long-range weapons tests.

Pyongyang has not tested intercontinental ballistic missiles or nukes since 2017, and has continued to observe a self-imposed moratorium even after diplomacy with the United States stalled.

- 'Offensive weapons' -

The North's saber-rattling comes at a delicate time in the region, with Kim's sole major ally China set to host the Winter Olympics next month and South Korea gearing up for a presidential election in March.

"The Kim regime is developing an impressive diversity of offensive weapons despite limited resources and serious economic challenges," said Leif-Eric Easley, a professor at Seoul's Ewha University.

"Certain North Korean tests aim to develop new capabilities, especially for evading missile defenses," he added.

"Other launches are intended to demonstrate the readiness and versatility of missile forces that North Korea has already deployed."

After a decade in power, leader Kim has little to celebrate, with a Covid-battered economy causing food shortages at home, diplomacy with the United States stalled and biting sanctions taking their toll. 

That may explain why North Korea has carried out five weapons tests in the last three weeks, analysts said earlier in the week -- and a dramatic demonstration of the nuclear-armed country's military prowess offers a quick win ahead of important domestic anniversaries.

The country is preparing to mark the 80th anniversary of the birth of Kim's father, late leader Kim Jong Il, in February, as well as the 110th birthday of the country's founding leader Kim Il Sung in April.

It may also be looking to conduct tests ahead of the start of the Beijing Winter Olympics next week, lest it anger its sole major ally China by raining missiles on its parade.