"Norway is a coastal and maritime nation, and submarines are absolutely essential to the defence of our country. We are seeing an increase in the activity of Russian forces in the North Atlantic and the Barents Sea," Defence Minister Tore Sandvik said in a statement announcing the multi-billion dollar purchases.

Norway has a 198-kilometre (123-mile) land border with Russia, which is fighting a protracted war in Ukraine, as well as a maritime border in the Barents Sea.

The government had already ordered four submarines from German firm Thyssenkrupp Marine Systems in 2021 and the first of those is to be delivered in 2029, the ministry said in the statement.

"As NATO's 'eyes and ears' in the North, this requires a greater capacity to show our presence, to monitor and to deter in our immediate vicinity. In this context, submarines are absolutely indispensable," Sandvik added.

The government proposed increasing the defence budget by 46 billion krone ($4.5 billion) because the cost of submarines and their arms systems had increased.

In a separate statement, the defence ministry said 19 billion krone would be spent on missiles able to reach targets up to 500 kilometres (300 miles) away.

The ministry did not say which missiles would be bought but the NTB news agency said the US Himars system, South Korea's Chunmoo missiles and a system made by Germany's KNDS group were being considered.