SEOUL - A South Korean provincial governor of the main opposition party narrowed a gap with frontrunner of the same party in recent presidential polls.

According to a Realmeter survey released on Monday, Ahn Hee-jung, governor of South Chungcheong Province who is affiliated with the Minjoo Party, gained 20.4 percent in approval scores last week, up 3.7 percentage points from the previous week.

The result is based on a survey of 2,521 voters conducted between last Monday and Friday. It has 2.0 percentage points in margin of error.

Ahn's approval rating topped 20 percent for the first time, keeping an upward momentum for four straight weeks as supporters for former UN chief Ban Ki-moon moved to him following Ban's drop in presidential bid earlier this month.

Ahn has recently gained support from conservative voters as he indicated his willingness to create a coalition with the ruling Liberty Korea Party and other conservative politicians if he is elected the next president.

However, his core supporters in the opposition bloc are believed to have turned their backs for his conservative-leaning disposition. It is expected to serve as disbenefit to him in the Minjoo Party's primary to select the party's official presidential candidate.

Ahn narrowed a gap with the frontrunner Moon Jae-in, former head of the Minjoo Party who won 32.5 percent in support scores last week. Moon kept the top spot for the seventh consecutive week, but the figure was down 0.4 percentage points from the prior week.

Prime Minister Hwang Kyo-ahn, who is serving as acting South Korean president following the impeachment of President Park Geun-hye, maintained a third place but saw his approval rating fall to 14.8 percent compared with 15.3 percent in the previous week.

Hwang has been considered the best presidential contender in the governing party, of which public support sank with the presidential impeachment over the corruption scandal.