The South Korean side expressed doubts about North Korea’s response to the US "declaration of war" counterattack measures.
CCTV News:North Korea’s Foreign Minister Li Yonghao told the media in new york on 25th that US President Trump "has declared war on North Korea" and that North Korea will have the right to take counter-measures including shooting down American bombers.

DPRK Foreign Minister Li Yonghao
South Korea expressed doubts about North Korea’s ability to respond. The chairman of the South Korean Congressional Intelligence Committee said that when the US bomber flew near the eastern waters of North Korea on the 23rd, North Korea did not make any response.
According to Yonhap News Agency, Lee Jae-woo, chairman of the South Korean Congressional Intelligence Committee, said on the 26th that according to the report of the relevant person in charge of the South Korean National Intelligence Agency, when the US strategic bomber formation flew in the international airspace in the eastern waters of North Korea on the 23rd, the DPRK may not have anticipated it at all, and the radar and other related systems may not have noticed it, so it failed to take immediate measures. Afterwards, the DPRK dispatched planes to strengthen its vigilance against the east coast.
Li Zheyu, chairman of the South Korean Congressional Intelligence Committee, said that it was midnight, and North Korea did not expect it at all. The radar did not find the target and failed to take any measures.

RC-135 reconnaissance plane
However, CBS believes that although the US bomber’s action this time is 200 miles (about 322 kilometers) away from the North Korean coastline, it has exceeded the effective range of North Korean air defense missiles. But if North Korea tries to intercept it, it will be extremely dangerous.

Video screenshot: The pilot gestures in his cockpit.
In 2003, an RC-135 reconnaissance plane of the US military was intercepted by four North Korean fighter planes while cruising in Japan. In the video released by the Pentagon, people can see a North Korean fighter pilot gesturing in his cockpit, apparently asking the US reconnaissance plane to leave this airspace.

The picture of EC-121 reconnaissance plane comes from the network.
A more painful lesson occurred in 1969, when an American EC-121 reconnaissance plane was shot down by a North Korean fighter plane, killing more than 30 Americans on board.
South Korean experts believe that due to the low possibility of shooting down American bombers, the "all defensive countermeasures" mentioned by North Korean Foreign Minister Li Yonghao may refer to the siege of Guam.
On 26th, Dunford, Chairman of the Joint Chiefs of Staff of the US Army, testified before the Armed Services Committee of the Senate, saying that the United States has intensified its intelligence gathering on the DPRK over the past year and a half, and judging from the recent movements of the DPRK military, there is nothing special about it.
Ministry of Foreign Affairs of China: Military means should not be an option to solve the nuclear issue on the peninsula.

On September 27th, China’s Foreign Ministry spokesman Lu Kang said, we always believe that military means should not be the option to solve the nuclear issue on the peninsula, because military force can’t solve differences, but it will only lead to greater disasters, which are unacceptable to all parties. We hope all parties concerned can avoid taking measures that intensify contradictions and may lead to further escalation of the situation.