Ranking lawmakers of South Korea's ruling Saenuri Party expressed concerns Wednesday that North Korea could carry out its fourth nuclear test and other provocations in the wake of the execution of leader Kim Jong-un's uncle.

The remarks echoed growing concerns among South Korean government officials that North Korea may launch a provocation to divert domestic attention away from Jang Song-thaek's execution to external issues.

Rep. Won Yoo-chul, who chairs the ruling party's special committee for security strategies against North Korea's nuclear program, told a meeting of senior party lawmakers and Supreme Council members that the likelihood of a fourth nuclear test or another long-range missile test "could become very large" if the communist regime continues its reign of terror.

He also urged the government and military to prepare against any contingencies and step up their security posture and monitoring of North Korea.

Jang, long considered the second most powerful man in the North, was executed for treason last week, sparking fears of political instability in the totalitarian nation.

Rep. Yoo Ki-june of the ruling party said the execution may be used as a means to consolidate power around Kim and strengthen internal unity, but the effects are not expected to last.

"Over time, there is a large possibility that it will lead to public disaffection and distrust of the regime, so we need to watch the North's movements and draw up countermeasures," Yoo said at the meeting.

Six-term lawmaker Rhee In-je raised concerns that a fourth nuclear test may be "inevitable" if North Korea's aim is to maintain the current regime by strengthening its nuclear capabilities.

On Tuesday, Rep. Cho Won-jin, a ruling party lawmaker and ranking member of the parliamentary intelligence committee, said North Korea is showing signs of preparations to carry out its fourth nuclear test and another long-range rocket launch. He provided no further details.

North Korea has conducted three nuclear tests so far, the first in 2006, second in 2009 and third in February. Pyongyang has also carried out a series of long-range rocket launches, including the latest one in December last year, in a widely believed attempt to develop nuclear missiles.

Pyongyang has said its rocket launches were for peaceful purposes. (Yonhap News)