British defense officials say they have practiced cyber war games that could shut off electricity in Russia’s capital, the Sunday Times (paywall) reports.

The measures are part of a wider range of strategies to hit back at an increasingly assertive Russia—accused of interfering with US elections, cyberattacks on Western targets, and poisoning a former spy on UK soil—without resorting to a full-blown nuclear attack.

“If they sank our aircraft carrier with a nuclear-tipped torpedo, what is our response? There’s nothing between sinking their submarine and dropping a nuclear weapon on northern Kamchatka,” one senior source told the Sunday Times. “This is why cyber is so important; you can go on the offensive and turn off the lights in Moscow to tell them that they are not doing the right things.”

Military planners are looking for options if Russian president Vladimir Putin tests NATO’s resolve by seizing small islands belonging to Estonia, taking control of Libya’s oil reserves, or using ”irregular forces” to attack troops, according to the report.

British troops also recently held their biggest military exercise in 10 years, which included six navy ships and more than 5,000 troops in the Omani desert, to prepare for a confrontation with unconventional Russian forces like those used in Crimea. Cyber weapons are seen as a potential deterrent and a way to avoid a direct military confrontation.

UK defense chiefs are talking up their cyber prowess after a string of alleged Russian hacker exploits, including revelations last week of a Russian computer attack on the international chemical weapons watchdog. The attempted hack was disrupted by Dutch military intelligence with the help from British officials. Also last week, US authorities charged Russian intelligence officers with seeking to hack the nuclear energy company Westinghouse Electric and anti-doping watchdogs.

The announcements suggest world leaders are pushing back against Putin’s increasing aggressive cyber operations, which allegedly includes breaking into the control rooms of vital US electric grids (paywall). Russia, after all, has hammered smaller nations with its cyber weapons in the past. The country disabled computer systems for the Estonia’s parliament, broadcasters, and banks in 2007, according to the Times, and regularly disrupts Ukrainian banking and electrical systems.

The US is expected to announce that it will use its cyber capabilities on behalf of NATO if asked, Reuters reported last week. The US announcement is aimed squarely at Russia, according to a senior defense official, and is part of a British-led effort to stiffen NATO’s cyber capacity. The 29-nation alliance has recognized cyber as a domain of warfare since 2014, but the precise implications haven’t been formalized.

American intelligence shows that Russian hackers broke into the Democratic National Committee and leaked information in the lead-up to the US presidential election. The White House recently warned foreign entities that it would use more offensive measures as part of its revised cyber security strategy. US intelligence reportedly expects a series of hacker attacks before congressional elections next month.