SEOUL, South Korea -- North Korea fired dozens of artillery shells toward its disputed sea border with South Korea on Wednesday, apparently to emphasize that the peninsula remains a war zone and push for a treaty to formally end the Korean War -- a key demand of the nuclear-armed North.
Such a strategy, however, appears to have little chance of success as South Korea and the United States have insisted that Pyongyang return to international talks aimed at its denuclearization in exchange for aid and security guarantees before any treaty can be concluded.
South Korea immediately responded Wednesday with 100 warning shots from a marine base nearby after the North fired about 30 artillery rounds into the sea from its western coast in the morning, according to the South's Defense Ministry and Joint Chiefs of Staff.
No casualties or damage were reported, as the North's volleys landed in its own waters while the South fired into the air, the officials said.
It was the first exchange of fire between the two Koreas since a naval skirmish in November that killed one North Korean sailor and wounded three others. Wednesday's volleys by the North appeared aimed at raising tensions, and the likelihood of wider fighting seemed dim as long as the two sides show restraint.
The North resumed firing later Wednesday but the South didn't respond after issuing two warning broadcasts, two ministry and JCS officials said on condition of anonymity because of department policy.
South Korea's Yonhap news agency reported that the North is believed to have fired a total of about 100 artillery rounds throughout the day.
The western sea border -- drawn by the American-led U.N. Command at the close of the 1950-53 Korean War -- is a constant source of tension between the two Koreas, with the North insisting the line be moved farther south.
Besides November's clash, the two sides engaged in bloody naval skirmishes in 1999 and 2002.
The disputed area is a rich fishing ground. Boats from the two Koreas jostle for position during the May-June crab-catching season, and South Korea sometimes repatriates North Korean fishermen who stray into southern waters. The North also deliberately sends its warships across the border it feels was wrongly demarcated, while South Korean navy vessels routinely carry out patrols in the area.
The North's military said in a statement later Wednesday that it had fired artillery off its coast as part of an annual military drill and would continue doing so.
South Korean officials said the North designated two no-sail zones in the area, including some South Korean-held waters, from Monday through March 29, a possible indication the North may fire more artillery or even conduct missile tests. The North in December had designated an artillery "firing zone" along disputed the sea border.
Analysts say the North's show of firepower is primarily aimed at stoking military tension on the peninsula, thus sending a message to the U.S. about its demands for the signing of a Korean War peace treaty.
"North Korea is staging armed protests toward the U.S. to call for the urgency of signing the peace treaty," said Kim Yong-hyun, a North Korea expert at Seoul's Dongguk University.
Such a treaty is a coveted goal of Pyongyang, which argues it was compelled to develop nuclear weapons to cope with what is sees as a U.S. threat.
Washington and Pyongyang have never had diplomatic relations because the 1950-53 Korean War ended in a truce, not a peace treaty, leaving the peninsula technically at war. North Korea, the U.S.-led United Nations Command and China signed a cease-fire, but South Korea never did.
Earlier this month, the North announced its return to nuclear disarmament talks it quit last year hinges on improved ties with the U.S., including the signing of a peace treaty, and the lifting of sanctions. Washington and Seoul, however, have brushed aside the North's demands, saying it must first return to the disarmament negotiations and report progress in denuclearization.
Concluding a treaty would "remove the danger of outbreak of war and create atmosphere favorable for the denuclearization" the North's government-run Minju Joson newspaper said in a commentary carried by the official Korean Central News Agency Wednesday.
Yoo Ho-yeol, a professor of North Korean studies at Korea University in South Korea, said Pyongyang was also stoking military tensions to express anger over South Korea's lukewarm response to recent gestures seeking dialogue.
North Korea has sent a series of mixed signals to the South, balancing offers of dialogue on economic cooperation with military threats. South Korean Defense Minister Kim Tae-young, meanwhile, angered Pyongyang by saying Seoul's military should launch a pre-emptive strike if there was a clear indication the North was preparing a nuclear attack.
South Korea's Defense Ministry sent the North's military a message Wednesday expressing serious concern about the artillery firing and saying it fostered "unnecessary tension" between the two sides.
South Korean Unification Minister Hyun In-taek criticized Pyongyang for raising tension, but also said Seoul has no intention to cancel talks next week about a joint industrial complex in the North.
The Unification Ministry also intends to push ahead with a plan to send 10,000 tons of food aid to North Korea in what would be Seoul's first direct humanitarian assistance in about two years, according to a ministry official who spoke on condition of anonymity citing department policy.
Korea University's Yu said that tensions are expected to last for some time.
"But it remains to be seen whether more serious military conflicts will take place," he added.
Despite the exchange of fire, the capitals of the two Koreas were calm Wednesday.
North Koreans in Pyongyang wearing thick winter coats walked briskly through the streets while a female police officer directed traffic and passengers rode on a crowded tram through the city, according to footage shot by broadcaster APTN.
The military tensions had little effect on South Korean financial markets. Seoul's benchmark stock index closed less than 1 percent lower for the day, while South Korea's currency, the won, rose against the U.S. dollar.
Associated Press writer Yewon Kang contributed to this report.