South Korea's President, Lee Myung-Bak, has said his government will stand firm in the face of threats from the North.
The commander of US forces in South Korea has said he has not ruled out a military response if North Korea test-fires a long-range missile.
North Korea is reported to be preparing to test-fire a long-range missile, and recently scrapped peace accords with the South.
US General Walter Sharp urged North Korea to cease what he referred to as provocations, and behave like a responsible country.
Mr Lee said that though his ministers were always ready to talk with North, they would not rush into dialogue.
North Korea is reported to be preparing to test-fire a long-range missile.
Mr Lee has taken a harder line than his predecessors on relations with the North since he took office a year ago.
South Korea's President, Lee Myung-Bak, has also said he will stand firm in the face of threats from the North.
He added that trying to be nice from the start could mean ending-up with poor results.
Tension in the Korean peninsula has risen in recent weeks - with the North warning that it considers itself on the brink of war with the South.
His comments came ahead of a confirmation hearing for his new Unification Minister, Hyun In-Taek, who North Korea has denounced as "anti-DPRK [North Korea] confrontational fanatic and sycophantic traitor serving the US".
Satellite evidence
Do not panic
According to the South Korean media, recent satellite spy photos show a large cylindrical object being moved towards North Korea's long-range missile site.
The South is the only country in the entire world that is sincerely concerned for [North Korea's] future and willing to help it Lee Myun-bakSouth Korean President "I am very aware there are people who are concerned about the recent series of North Korean threats. But you do not need to worry too much," the president said in his regular radio address.
North Korea carried out a "failed" Taepodong-2 missile test in 2006Speaking at a press conference for foreign journalists, General Walter Sharp - the commander of the more than 28,000 American troops stationed in South Korea - said he would not confirm what is, or is not, known by intelligence sources.
"The government is ready to sit down with North Korea at any time and resolve every issue," Mr Lee said.
But when asked what he would do if North Korea was to proceed with a long-range missile test, he said: "We have all available options open to us".
Mr Lee said his government would not repeat the mistakes of his predecessors by rushing into dialogue.
"That includes everything from diplomatic to economic sanctions, to military options," he said.
"I believe it is better to start off with a little difficulty, but ensure things are set right to reach a positive outcome, instead of trying to figure out what North Korea wants while saying all is well that ends well," he said.
"Of course we very much want the military option to be the last to be taken but those options are all open to us."
North Korea's last long-range missile test in 2006 was met with international condemnation and UN sanctions, but no military action.
RECENT TENSIONS Dec 07: Lee Myung-bak wins South Korean presidential election. Vows tougher line on the NorthMarch 08: North expels S Koreans from joint industrial park after Seoul says it will link its aid more closely to the nuclear disarmament issueApril 08: N Korean media warns President Lee his tough stance could have "catastrophic consequences"July 08: Pyongyang rejects President Lee's offer of direct talksOct 08: Military officials from both sides hold first direct talks since President Lee took officeNov 08: N Korea says it will close land borders, suspend tourism trips and the joint train service because of "relentless confrontation" from SeoulDec 08: N Korea enforces stricter border controls and expels hundreds of South Koreans from the joint industrial zoneJan 09: The North says it is scrapping all military and political pacts signed with the South
Diplomatic tension has been rising in recent weeks, with increasingly angry rhetoric coming from North Korea, warning that relations with the South have reached what it called "the brink of war".
Some analysts believe this is mere posturing as an attempt to strengthen its negotiating position with the new US administration.
But inter-Korean relations have steadily deteriorated significantly since the conservative Mr Lee took office in Seoul in February last year.
Mr Lee said on Monday that though his ministers were always ready to talk with North, they would not rush into dialogue.
"We are ready to work with North Korea. North Korea, too, must realise the South is the only country in the entire world that is sincerely concerned for its future and willing to help it," Mr Lee said.
"We are ready to work with North Korea. North Korea, too, must realise the South is the only country in the entire world that is sincerely concerned for its future and willing to help it," Mr Lee said.
Inter-Korean relations have steadily deteriorated since the conservative president took office in Seoul in February last year.
His comments came ahead of a confirmation hearing for his new Unification Minister, Hyun In-Taek, who North Korea has denounced as "anti-DPRK [North Korea] confrontational fanatic and sycophantic traitor serving the US".
Mr Lee has reversed the "sunshine" policy which gave unconditional aid to the North, insisting that all major economic assistance would depend on the North's willingness to scrap its nuclear weapons programme.
North Korea said if Mr Huyn was confirmed in the job, inter-Korean relations would collapse into ruin.
Outrage
North Korea has expressed outrage at the change in approach. RECENT TENSIONS Dec 07: Lee Myung-bak wins South Korean presidential election. Vows tougher line on the NorthMarch 08: North expels S Koreans from joint industrial park after Seoul says it will link its aid more closely to the nuclear disarmament issueApril 08: N Korean media warns President Lee his tough stance could have "catastrophic consequences"July 08: Pyongyang rejects President Lee's offer of direct talksOct 08: Military officials from both sides hold first direct talks since President Lee took officeNov 08: N Korea says it will close land borders, suspend tourism trips and the joint train service because of "relentless confrontation" from SeoulDec 08: N Korea enforces stricter border controls and expels hundreds of South Koreans from the joint industrial zoneJan 09: The North says it is scrapping all military and political pacts signed with the South
News reports quoting unnamed intelligence sources suggested last week that North Korea is making moves to test its Taepodong-2 missile.
North Korea may also fire short-range missiles toward a disputed sea border with the South to raise tension, the reports suggested.
Talks between North Korea, the US, China, Russia, Japan and South Korea have stalled amid US demands for more verification of North Korea's nuclear arsenal.
Hard line?
Mr Hyun, meanwhile, faces a tough confirmation hearing, as South Korean opposition legislators question his ability to tackle mounting tensions with the North.
He is a professor of political science at Korea University in Seoul, and was the major architect behind the Lee administration's North Korea policy, which pledged to help Pyongyang raise domestic incomes to $3,000 (£2,000) on the condition that it abandon its nuclear programme.
"It is not true that the 'Denuclearization, Openness, 3000' campaign is purely a conservative, hardline policy, as many seem to believe," he told parliament on Monday, Yonhap reported.
"It's a policy of co-existence and co-prosperity for both South and North Korea," Mr Hyun said.
North Korea, however, remained unmoved, saying if Mr Huyn was confirmed in the job, inter-Korean relations would collapse into ruin.
