Artur Zakharov, Estonian Defense Forces (EDF) spokesperson, said: "At the moment, it is not viable to talk about the final state of those who arrived, since the call-up's formation is still in progress," said.

"However, the speed of the reservists and their will to defend are impressive, as, for example, as of 6 p.m. yesterday, less than nine hours after the announcement of the additional training gathering, more than half of the invited reservists had already arrived," he went on.

The personnel will undergo further training, while the erection of a temporary barrier on Estonia's largely undefended southeastern border – one of the main activities the exercise is being tasked with – is to start in the next few days, Zakharov went on.

A more precise number than around half has not been mentioned yet; 1,684 people have been summonsed, meaning around 800 are likely to have turned to already, based on what the EDF is saying.

The exercise is dubbed Okas ("quill") in line with other snap exercises, which are also often so-named, while the 20th and 27th Pioneer Battalions and the 191st and 291st Intelligence Companies are the main units affected by the call-up.

The barrier will stretch around 40 km, with razor wire to be installed in areas the Police and Border Guard Board (PPA) adjudicates to be most at-risk, while those reservists already with their units are already undergoing training, including acquaints with the R-20 Rahe rifle, which only started to arrive in significant numbers over the past year.

Conscription, held over two intakes per year, is mandatory in Estonia, with exemptions for university students and some other categories, and while conscripts serve either an eight-month or an 11-month stint, they are placed on reserve lists after completing their term and subject to regular call-ups in the ensuing years.

Reservists are not to be confused with the volunteer Defense League (Kaitseliit), which augments the regular EDF and is made up of people who serve in their spare time, while the EDF also contains regular officers and soldiers who were not conscripted. The air force (Õhuvägi) holds no rounds of conscription.

Reservists whose units are involved in the exercise are required to immediately come to a meeting point outlined in the call-up. Reservists can check whether they are included in the additional training from the register of conscripts here.

Latvia is also holding military drills on its border with Belarus, public broadcaster LSM reported this week.