SEOUL, April 20 (Xinhua) -- The second TV debate of five major South Korean presidential candidates focused on issues related to security and the Democratic People's Republic of Korea (DPRK) amid tensions on the Korean Peninsula.

During the second TV debate, broadcast Wednesday night, four candidates showered questions at Moon Jae-in of the biggest Minjoo Party, a frontrunner in polls who has maintained an engagement policy toward the DPRK.

Moon is the former chief of staff to late President Roh Moo-hyun who met in 2007 with late DPRK leader Kim Jong Il, the father of current top DPRK leader Kim Jong Un.

Hong Joon-pyo of the former ruling Liberty Korea Party, which had kept a hardline stance on the DPRK, criticized Moon for his argument for an expanded economic cooperation between the two Koreas. Hong denounced Moon as a pro-DPRK follower and a leftist.

In response, Moon said the expanded cooperation would economically benefit not only the DPRK but also South Korea, of which companies can do business with the northern neighbor. The companies will hire subcontractors, which in turn, employ more workers in South Korea.

Sim Sang-jung of the minor progressive Justice Party demanded Moon express a clearer stance on the installation of the U.S. Terminal High Altitude Area Defense (THAAD) missile defense on South Korean territory.

Regarding this, Moon reiterated his position that the final decision on THAAD should be made by the next government after going through appropriate procedures such as the parliamentary approval and public discussions.

Seoul and Washington agreed in July last year to deploy one THAAD battery in southeast South Korea. A THAAD battery is composed of six mobile launchers, 48 interceptors, an AN/TPY-2 radar and a fire & control unit.

On March 6, two mobile launchers and part of THAAD elements were delivered to a U.S. military base in South Korea, raising concerns about a hurried push for the deployment before a presidential election.

The presidential by-election is scheduled for May 9 as former President Park Geun-hye was impeached on March 10 over corruption allegations.

The hasty push for THAAD in South Korea caused strong oppositions from regional countries, including China and Russia, as it breaks regional strategic balance and damages security interests of the two countries.