North Korea fired four short-range ballistic missiles toward the sea, South Korean officials said on Saturday,amid rising tensions in the Korean Peninsula. 

The missiles flew around 130 kilometers (80 miles) toward the North's western sea, said South Korea's Joint Chiefs of Staff.

Pyongyang has launched a series of missiles this week, raising concerns that it could be preparing to resume nuclear testing for the first time since 2017.

North Korea's Foreign Ministry said late Friday that its recent military actions were in response to combined aerial exercises currently being conducted by the US and South Korea.

B-1B bombers fly over South Korea

Saturday's launches were reported just hours after Seoul said a US supersonic bomber, the B-1B, would fly over South Korea as part of their joint drills.

The "Vigilant Storm" exercises, which began on Monday, involved some 240 warplanes, including advanced F-35 fighter jets from the US and South Korea. 

The drills were initially scheduled to run until Friday, but they were extended to Saturday as Seoul scrambled jets after detecting the mobilization of 180 North Korean warplanes.

South Korea's Defense Ministry said two B-1B bombers participated on the last day of the exercises.

The deployment of US strategic weapons has long irritated North Korea. Pyongyang describes the B-1B as a "nuclear strategic bomber," but the plane was switched to conventional weaponry in the mid-1990s.

The B-1B planes were last deployed in the region in 2017, when tensions were rising amid another series of weapons demonstrations from North Korea. 

In recent years, the US and South Korea had halted their exercises, including such show-of-force flyovers, as former US President Donald Trump sought a different approach toward the regime in Pyongyang. 

How have allies reacted to recent escalation?

South Korea, Japan and the US have strongly condemned the North's recent missile launches. South Korean officials have warned that there are indications Pyongyang could detonate a nuclear test device in the coming weeks. 

German President Frank-Walter Steinmeier, who is currently visiting South Korea, criticized the North for jeopardizing international security. He called on Pyongyang to resume talks.

Meanwhile, Pyongyang's allies Moscow and Beijing have blamed Washington for the recent escalation. 

During a UN Security Council emergency session on Friday, US Ambassador Linda Thomas-Greenfield dismissed criticism of the US-South Korea excercies as North Korean "propaganda." 

fb/nm (AFP, AP, Reuters)