The 15-member council on June 12 imposed sanctions on the North following its May 25 nuclear test, banning all weapons shipments except small arms and authorising cargo inspections.
The council has since been discussing a list of entities, goods and individuals to be subject to the sanctions.
"Unlike before, the list they are working on will include North Korean individuals this time," a Seoul government official told AFP on condition of anonymity.
"You may say sanctions are toughening."
Previous sanctions targeted companies whose overseas assets were frozen, but not individuals.
The official did not say how many people would be on the list or who they were, adding that the Security Council was still in talks.
Local media has said they would likely include Ju Kyu-Chang, a National Defence Commission member supervising nuclear and missile development, and two nuclear scientists -- So Sang-Kuk of Kim Il Sung University and Li Yong-Ha of Yongbyon Physics University.
"Nothing is agreed until everything is agreed," the official said, in response to media reports that 15 people would face travel bans and a freeze on any overseas assets.
However he said there was a "strong sentiment" that the list should be finalised no later than Wednesday New York time, to meet an extended deadline of July 19.
Since a long-range rocket launch in early April, the North has staged its second nuclear test, fired a variety of shorter-range missiles, renounced the truce in force on the Korean peninsula and quit nuclear disarmament talks.
US and South Korean officials believe ailing leader Kim Jong-Il, 67, is staging a show of strength to bolster his authority as he tries to put in place a succession plan involving his youngest son Jong-Un.
Source: AFP Asian Edition