President Park Geun-hye paid tribute Thursday to the dozens of fallen soldiers who died in a North Korean torpedo attack five years ago, saying she will build a strong defense posture to prevent similar tragedies.

On March 26, 2010, the 1,200-ton warship Cheonan sank near the western maritime border with North Korea, killing 46 of the 104 sailors on board. A South Korean-led investigation, including experts from the U.S., Australia, Britain and Sweden, concluded that the corvette was downed by a North Korean torpedo, but Pyongyang has denied any responsibility.

Speaking at a memorial ceremony in Daejeon National Cemetery, 164 kilometers south of Seoul, Park vowed to push for reunification of the two Koreas to honor the fallen soldiers.

"The government will expand our national defense capabilities and establish a firm war deterrent based on our solid alliance with the United States, and ensure that incidents similar to the attack on the Cheonan never happen again," Park said in her address to the more than 5,000 people gathered, including the bereaved families, survivors, top government officials and citizens.

She also ordered the military to be on the alert against unexpected provocations and block all such possibilities.

"I hope North Korea also abandons its reckless provocations and belief that nuclear weapons can protect it," Park said. "Only when North Korea abandons its isolation and stagnation for the road to true change will we be able to build a new Korean Peninsula."

This year marks the 70th year since Korea gained independence from Japanese colonial rule and came under U.S. military occupation in the South and Soviet occupation in the North.

"Realizing a unified homeland where people of both the South and North are happy is sure to be an earnest wish of our patriotic martyrs and a way to ensure that the sacrifices of the Cheonan soldiers were not in vain," Park said.

South Koreans across the country marked the anniversary with memorial ceremonies, photo exhibitions, concerts and marches.

In the southeastern port city of Busan, more than 3,000 students and citizens are expected to gather at a square to commemorate the anniversary.

The Navy is also scheduled to hold meetings and carry out drills at each unit. (Yonhap)