SEOUL, South Korea (CNN) -- North Korea denied on Tuesday that a body found on a South Korean beach was one of its agents while South Korean troops combed the east coast area in search of more infiltrators.

"We have nothing to do with the incident," the official Korean Central News Agency (KCNA) quoted a North Korean spokesman as saying. The report was monitored in Tokyo.

It was the first comment made by the reclusive North since South Korea reported finding a corpse in a wetsuit along with a Czech-made machine-gun, hand grenades and other equipment along with a torpedo-shaped diver's propulsion vehicle.

An oxygen tank with three mouthpieces found beside the dead diver sparked a South Korean military manhunt for other possible infiltrators.

Meanwhile, more troops were trucked and flown to South Korea's jagged east coast Tuesday to join in what officials feared would turn into a prolonged hunt for other possible North Korean infiltrators.

Officials believe at least two other North Korean agents either drowned or managed to come ashore and might be trying to return to the North by land.

After three days of fruitless searching, Defense Ministry officials said they were moving in more soldiers along a rocky mountain range that runs to the North Korean border -- a possible escape route offering a multitude of hiding places.

"All measures are being taken to expand the dragnet and block the likely escape routes on the east coast," said Col. Hwang Dong-kyu, a spokesman for the Joint Chiefs of Staff.

"We believe this is going to take some time," said a Defense Ministry spokesman, Oh Jong-seok. "We are prepared for a long search."

North Korea accused South Korean ultrarightists of staging the incident to sabotage President Kim Dae-jung's policy of accommodation and cooperation with the North.

South Korea said it lamented the North's "deceitfulness" and demanded an immediate apology along with a pledge to halt further intrusions.

With a dusk-to-dawn curfew in force on the east coast, soldiers and police laid ambushes or searched rugged mountains and deep valleys in a growing radius from Donghae, 195 kilometers (117 miles) east of Seoul, where the body was first discovered.

A Defense Ministry spokesman declined to say how many troops had been committed to the search, but said the force had been increased by 50 percent Tuesday.

It was the third North Korean infiltration reported along the east coast, coming less than three weeks after a northern submarine was found tangled in a fishing net on June 22.

Nine bodies were found in the small sub, all shot to death in what military investigators described as a murder-suicide committed by senior officers to avoid capture.

On September 18, 1996, a larger North Korean submarine was found stranded in the same general area, touching off a 53-day manhunt for the craft's 26 occupants.

The manhunt by 60,000 soldiers, reservists and police left 37 people dead -- 24 North Koreans and 13 South Koreans -- and sent relations between North and South Korea plunging to their lowest level in years.

The latest incursion put a strain on President Kim Dae-jung's policy of trying to open up the North's reclusive society through expanded civilian economic, cultural and personal exchanges.

Kim was to convene a full national security meeting Wednesday to discuss specific South Korean countermeasures as his conservative opposition criticized his policy as too naive.

The two Koreas remain technically at war after their 1950-53 conflict ended with only an armistice, not a peace treaty.

The Associated Press and Reuters contributed to this report.