Updated

North Korea began restricting traffic through two checkpoints in its tightly sealed border with South Korea on Monday — punishment for Seoul's hard-line stance toward the communist regime.

The restrictions forced the suspension of two landmark reconciliation projects — cross-border train service and tours to the North's historic border city of Kaesong — setting back a decade of rapprochement efforts between the Cold War rivals.

North Korea also ordered a sharp cut in the number of South Koreans permitted to stay in a joint industrial complex in Kaesong to 880 — a fifth of the 4,200 with permits for the enclave and about half the number there on an average workday, Seoul's Unification Ministry said Monday.

The cutback is expected to affect 88 South Korean companies that run factories in Kaesong employing 35,000 North Koreans.

"Of course it's a nuisance. We could leave the complex at our convenience, and now that they're restricting our entry, I foresee some difficulties arising," Ahn Young-su, a South Korean manager in Kaesong, said at a border checkpoint.

The setbacks in those projects come on top of the suspension of another key reconciliation project — tours to the North's scenic Diamond Mountain that were brought to a halt after a North Korean soldier fatally shot a South Korean tourist there in July.

"It is very regrettable that North Korea has imposed restrictions on border crossings," Unification Ministry spokesman Kim Ho-nyeon said. "The North's measure should be immediately withdrawn."

The border between the Koreas is tightly sealed, with hundreds of thousands of heavily armed troops amassed on both sides. But the two sides opened two corridors across the border as they sought reconciliation under South Korea's two previous liberal presidents.

Tensions have been high since conservative South Korean President Lee Myung-bak took office in February with a pledge to seek a tougher approach to the North than his liberal predecessors.

Lee has questioned implementing key accords his predecessors struck with North Korean leader Kim Jong Il that call for providing aid to the North without condition. That and other moves by Seoul, including its recent sponsorship of a U.N. resolution denouncing North Korea's human rights record, have enraged the North.

North Korea accuses Lee of seeking confrontation.

The 1950-53 Korean War ended with a truce, not a peace treaty, leaving the two Koreas technically at war. Ties warmed significantly following the first-ever summit of their leaders in 2000, but chilled again this year with Lee's election.

On Monday, North Korea's main Rodong Sinmun newspaper blamed the South for the tension.

"The fate of the inter-Korean relations entirely depends on the attitude of the authorities of the South side," it said in commentary carried by the North's official Korean Central News Agency.