Inter-Korean communication lines were in normal operation Tuesday despite an angry statement that North Korea issued against joint military exercises between South Korea and the United States, officials said.

Kim Yo-jong, sister of North Korean leader Kim Jong-un, issued the statement expressing "deep regret" to South Korea for going ahead with the exercise with the US after she warned earlier that the maneuvers will cloud inter-Korean relations.

Despite the statement, the two Koreas held daily phone calls via their liaison hotlines, including the military channels in the eastern and western border regions, according to officials.

The phone lines, which had remained severed for over a year, were restored late last month after President Moon Jae-in and the North's Kim Jong-un agreed to improve their chilled ties amid little progress in nuclear negotiations.

Whether and how to conduct the summertime exercise drew keen attention after Kim Yo-jong warned that the drills would dampen the conciliatory mood created in the wake of the restoration of the communication lines.

Sources have said the South decided to go ahead with the exercise in a scaled-back manner.

Earlier in the day, a preliminary exercise kicked off in the run-up to the main summertime drills which are scheduled for Aug. 16-26.