The South Korean government has warned local firms against shipping any strategic materials to North Korea following the UN resolution imposing sanctions on its missile program, officials said Wednesday.

The warning was sent last week to about 80,000 South Korean firms after the Security Council banned the sale and purchase of North Korean missiles and related technology, said the Ministry of Commerce, Industry and Energy.

"An email message was sent to nearly all trading firms last week, asking them not to violate the UN resolution," a ministry official told AFP.

The North's test-firing of seven missiles, which splashed down in the Sea of Japan (East Sea) on July 5, earned an international rebuke.

But the cash-strapped regime, which sees missiles as key to its defense and a lucrative export, rejected the resolution and vowed to push ahead with its missile program.

"International pressure is mounting to restrict exports of strategic items to North Korea," the ministry official said on condition of anonymity.

South Korean firms were also urged to be careful about shipping sensitive products to China and other countries that could be resold to North Korea, he said.

The ministry forecast tougher sanctions if the United States enacts legislation that would slap sanctions on foreign businesses or individuals trafficking with North Korea in technology relating to missiles or weapons of mass destruction.

The legislation was passed by the US Senate Tuesday.