North Korea on Monday flatly denied any connection to three crashed drones recovered in the South, and accused Seoul of "fabricating" a link in order to smear Pyongyang.

South Korea's defence ministry said last week it was convinced that three rudimentary unmanned aerial vehicles (UAV) recovered in recent weeks were of North Korean origin.

Wreckage of the drones was found in three different places, including Baengnyeong island near the rivals' disputed sea border.

The ministry said analysis of the debris had secured various pieces of "circumstantial evidence" that clearly pointed to North Korea.

In its first clear denial, the North's Committee for the Peaceful Reunification of Korea (CPRK) said the South's accusation was baseless.

"The enemy forces are further stepping up their slander and smear campaigns by fabricating the ridiculous drone incident," the CPRK said in a statement carried by the North's official KCNA news agency.

"It is a vicious attempt to fabricate a second Cheonan incident," the statement added, referring to the South Korean naval corvette, Cheonan, which sank with the loss of 46 lives in 2010 near the South's disputed Yellow Sea border with the North.

An investigation by a South Korean-led international commission concluded the vessel had been sunk by a torpedo from a North Korean submarine -- a charge Pyongyang has always angrily denied.

Pyongyang later called for a joint probe with Seoul into the allegations that the drones had been produced in the North.

An inspection group of the North's powerful National Defence Commission said in a separate statement Monday that Pyongyang was willing to make "everything clear," denouncing Seoul for fabricating the second and third Cheonan cases.

"It is an inveterate bad habit of the South Korean authorities to cook up shocking cases and kick up anti-DPRK (North Korea) confrontation hysteria by linking those cases with the DPRK whenever they are driven into a crisis," it said.

North Korea "remains unchanged in its stand to jointly investigate all cases including the Cheonan case as they claim the North was involved in them", the NDC inspection group said.

"If the South Korean authorities have no compunction, there will be no reason whatsoever for them to shun the just and reasonable claim made by the DPRK from the very day of the occurrence of the Cheonan case," it said.

All three UAVs recovered by South Korea were equipped with cameras.

Their memory chips contained pictures of border areas and the capital Seoul, including the presidential palace, although they were of low quality, the defence ministry said.

Their constituent parts were from various countries, including South Korea, the United States, Japan and China, and were all widely available.

However, any serial numbers had been "intentionally removed," the ministry said, adding that US forensic experts would help with further analysis of the drones.