Conservative Chancellor Friedrich Merz has made boosting Germany's threadbare military a key priority given the threat from Russia and US President Donald Trump's questioning of the traditional American security umbrella for Europe.

The drive for now aims to attract volunteers to the armed forces, but includes provisions for compulsory service in case numbers fall short.

As part of planned legislation due to be presented to cabinet next month, all young German men would have to fill out a questionnaire about their readiness and willingness to serve in the military.

The questionnaire would be voluntary for young women.

From 2028, all 18-year-old men would be required to undergo screening to determine their fitness for military service, whether they have shown an interest in joining the armed forces or not.

The planned law would also provide for compulsory military service to be reintroduced if deemed necessary because of the security situation, and provided parliament gives its explicit approval.

Conscription was officially suspended in Germany in 2011 under then chancellor Angela Merkel.

Merz has introduced sweeping plans to largely exempt defence spending from Germany's strict debt rules in a drive to build up "the strongest conventional army in Europe".

But the Bundeswehr, currently 180,000-strong plus 49,000 reservists, has been struggling to recruit.

This year the defence ministry expects 15,000 new recruits for military service, 5,000 more than last year.

The eventual aim is to have a total military strength of 460,000 -- made up of 260,000 active soldiers and 200,000 reservists.

For the moment the government says it plans to rely on volunteers to build up the ranks, and hopes for 40,000 new recruits per year by 2031.

It also wants to make military service more attractive, for example by offering training in new technologies and language courses.

Germany's northern neighbour Sweden reintroduced a limited form of conscription in 2017, seven years after abandoning it.