HALIFAX, Nova Scotia – The Russian government shut down a sizable portion of Latvia's public cellphone network during large-scale military exercises on its home soil in September, officials say, representing a new threat to European nations in both the size and sophistication of the attack.

Defense officials all along Russia's western border reported unusual activity during its "Zapad 17" exercises in September, which by some accounts involved 100,000 Russian troops. Finland, for example, noted an increase in cyberattacks on its government networks, though officials speaking privately wouldn't attribute them directly to Moscow.

Local news outlets in Latvia previously reported the cellphone outage at the time, though a top defense official confirmed new details to U.S. News on the sidelines of a security summit here.

"During Zapad, several mobile phone towers were basically jammed," Latvian State Secretary for Defense Janis Garisons says. He declined to say specifically how many towers were jammed but says they were all in the western portion of the country.

The Latvian military had observed Russia's employment of jamming systems in Ukraine previously but on a smaller and less technical scale, Garisons says, adding, "this is a new dimension of that."

Garisons declined to say why Russia might have targeted the western region of the country, near Russia's province of Kaliningrad, located on the Baltic Sea and separated from the mainland by the Baltic countries. Though it might have been a subtle message that the threat from Moscow is not limited to Latvia's border region.

Latvia, which was formerly occupied and annexed by the Soviet Union, joined NATO in 2004, bolstering its status as a key contributor to overseas wars in Afghanistan and training missions in Ukraine but also subjecting it to constant threats from Russian propaganda and electronic warfare attacks like this summer's jamming.

Its Ministry of Defense has begun training all of its forces, including its national guard, in how to wage counterinsurgency warfare in the case of conflict at home akin to the Russian-backed separatists in eastern Ukraine. Riga has also adopted new legislation that allows the ministry to deploy the armed forces to small insurgencies without having to wait for the parliament to declare war.

"In dealing with those kinds of threat metrics, the best deterrent is to say we will take action immediately," Garisons says. "What we saw in Ukraine was a lack of awareness and a lack of decisiveness."