SEOUL - South Korea is poised to step up security levels at the country's major airports ahead of the upcoming Nuclear Security Summit in Seoul, the government said Thursday.

The Ministry of Land, Transport and Maritime Affairs said security alert levels at four airports, including Incheon International Airport, the main gateway to South Korea, will be raised to "orange" level between March 19 and 22. ?

An orange alert is the second highest of a five-tiered system that progressively rises from "green" in a normal state to "blue," "yellow," "orange," and "red."

The ministry said a "red" alert will be issued between March 23 and 27.

"Passengers are expected to experience a little bit of inconvenience due to the tightening of security, but we hope they understand that it is an inevitable measure, given that the nuclear security summit is a large-scale international event," the ministry said in a statement.

Top leaders from 53 nations and four international organizations, including US President Barack Obama, Chinese President Hu Jintao and UN Secretary-General Ban Ki-moon, will attend the March 26-27 summit aimed at enhancing international safeguards and preventing nuclear terrorism.

It will be the second since Obama launched the global event in Washington in 2010.