Japan today threatened to shoot down a satellite that North Korea plans to launch early next month if it shows any signs of striking its territory.

Tokyo's warning that it would deploy its multibillion-dollar missile defence system raised tensions in the region after North Korea said that it had identified a potential "danger area" near Japanese territory along the rocket's flight path.

The regime told the International Maritime Organisation that the missile would be launched during daylight between 4 and 8 April, and that its boosters would fall into the Sea of Japan – about 75 miles (120km) from Japan's north-west coast – and the Pacific Ocean.

Officials in Tokyo said they reserved the right to destroy any threatening object in mid-flight, despite North Korean warnings that it would consider such a move an act of war.

"Under our law, we can intercept any object if it is falling towards Japan, including any attacks on Japan, for our security," Takeo Kawamura, the chief cabinet secretary, told reporters.

Despite repeated assurances from Pyongyang that the rocket is a vital part of North Korea's space programme, other countries in the region suspect the hardware is a Taepodong-2 ballistic missile.

South Korean intelligence has reported a build-up of activity in recent days near the missile's launch pad at Musudan-ri base on its neighbour's north-east coast.

Any missile launch, even one intended to put a satellite into orbit, would represent a snub to the US administration, which has repeatedly invited the communist state to return to negotiations over its nuclear weapons programme.

Last month the US secretary of state, Hillary Clinton, urged the north to cancel the launch, which US officials say would be in violation of a 2006 UN security council resolution.

The South Korean foreign ministry said in a statement: "If North Korea goes ahead with the launch, we believe there will be discussions and a response by the security council on the violation of the resolution."

The UN secretary-general, Ban Ki-moon, said a missile or satellite launch would "threaten the peace and stability in the region."

After Japan's transport ministry ordered airlines and shipping companies operating in the area to take precautionary measures, Japan Airlines and All Nippon Airways said they would alter flight paths on several European and other routes.

Speculation has been mounting for weeks that North Korea was about to put its hitherto unreliable missile technology to the test. The regime suffered a setback in 2006 when a Taepodong-2 missile – theoretically capable of reaching Alaska – blew up moments into its flight.

Japan has intensified efforts to protect itself against conventional missile attacks since 1998, when the north test-launched a long-range rocket over its territory without warning.

In response, Japan and the US have jointly developed a ballistic missile defence system that includes interceptor missiles on board ships and Patriot missiles dotted around Tokyo.

But experts believe that a rocket capable of launching a satellite into orbit may be too high to intercept.