South Korea will buy gas masks to protect residents of border islands against any North Korean chemical attack, officials said Thursday, as tensions remained high after last month's bombardment.

An official of the National Emergency Management Agency said it would supply an extra 1,300 gas masks to residents of the five frontline border islands, including Yeonpyeong, next year.

The North's November 23 shelling of Yeonpyeong killed two civilians and two marines, destroyed 29 homes and sparked a regional crisis.

"We'll make sure gas masks will be available to all residents of the five islands," the official told AFP on condition of anonymity, adding about 87 percent of them already have access to the masks.

The agency also plans to start supplying a further 610,000 gas masks over five years from 2012 to ensure that all the country's 3.93 million civil defence corps members have them.

The agency is also studying ways to renovate thousands of emergency shelters, including those in subway stations or underground car parks, to protect occupants against chemical weapons.

The South's defence ministry says the North has between 2,500 and 5,000 tons of chemical agents.

The island attack, the first on civilian-populated areas since the 1950-53 war, sparked outrage in the South, which is fortifying the islands.

Next year's budget approved Wednesday allocates an extra 261 billion won (229 million dollars) to deploy advanced weaponry and double troop numbers on them.

The military will install more anti-artillery radar, multiple-rocket launchers and precision-guided weapons on the Yellow Sea islands, after Seoul vowed to make Pyongyang pay "a dear price" for any future attacks.

The North defended its attack, saying the South's "puppet warmongers" provoked the incident to try to spark a wider conflict.

Pyongyang repeated claims it was merely retaliating for a South Korean military drill which had dropped "thousands of shells" into the North's waters.

Yeonpyeong is just south of the Yellow Sea border known as the Northern Limit Line, which was drawn by United Nations forces after the war.

The North does not recognise the line and says it should run further to the south. In a report Thursday, it said Yeonpyeong lies "deep inside" its territorial waters.

The South has said its troops were merely conducting a routine firing drill. But the North said the United States had engineered the incident, with the connivance of the South.

earlier related report
Russian jets entered airspace of US-Japan drill
Tokyo (AFP) Dec 8, 2010 - Two Russian military jets entered airspace over the Sea of Japan (East Sea) during a US-Japanese joint military exercise there this week, a Japanese government official said Wednesday.

A Japanese media report said the drills were temporarily halted as a result on Monday, but Moscow said "Russia did not commit any breaches of international rules on the use of airspace or of flight rules".

The United States and Japan have been conducting their biggest ever joint exercise, which comes after regional tensions spiked following North Korea's deadly artillery strike against the South two weeks ago.

The two Russian Il-38 patrol planes on Monday flew over the Sea of Japan, where the drill was taking place, Japan's top government spokesman Yoshito Sengoku said, confirming a report in the Sankei Shimbun daily.

Sengoku, the chief cabinet secretary, told a news conference that Japan immediately dispatched fighter jets to the area off the Noto Peninsula in central Japan but he gave no further details. A spokesman for Russia's Pacific Fleet, Roman Martov, told Interfax news agency: "The Il-38 planes mentioned in foreign media reports are serving in the Pacific fleet's marine aviation divisions.

"They were carrying out planned flights in the area of everyday activity for the fleet. Russia did not commit any breaches of international rules on the use of air space or of flight rules."

The massive US-Japanese "Keen Sword" war games include around 44,000 military personnel, 60 warships and 400 aircraft from both sides in a drill off Japan's southern islands, close to the South Korean coast.

The joint drills are larger than a naval exercise staged by Washington and Seoul last week, days after Pyongyang stunned the world with an artillery strike on a South Korean border island that killed four people.

Japan and Russia have quarrelled in recent months over a long-disputed island chain north of Japan's Hokkaido island which Soviet troops took in the final days of World War II.