These would be right up Putin's alley: nanoweapons are much smaller than a strand of human hair and the insect-like nanobots could be programmed to perform various tasks, including injecting toxins into people. DARPA is working on them and has successfully conducted tests in a hangar in Massachusetts. Russia and China are also believed to be working on related projects.
Previously, the Army Research Laboratory announced it created an advanced drone the size of a fly complete with a set of "tiny robotic legs" — a major achievement since it presumably might be capable of entering a building undetected to perform surveillance, or used for more nefarious actions.
Frightening details about military nanotechnologies were outlined in a 2010 report from the Pentagon's Defense Threat Reduction Agency, including how "transgenic insects could be developed to produce and deliver protein-based biological warfare agents, and be used offensively against targets in a foreign country."
While there are purportedly rules against using bioweapons, we know that Russia and North Korea have both targeted individuals for assassination by poison, most recently in the case of Kim Jon-Un's half-brother, who was taken out at an international airport last month. The NorKs are getting on a lot of peoples' nerves, and there has been some bandying about of a "preemptive strike" over there, which would certainly obligate the country's only ally, China, to get involved.
However, with the insect-like nanobots that DARPA has, it's entirely possible that the insane and paranoid dictator in North Korea could be selectively targeted without his knowledge; they could conceivably discharge an inhaled substance and simply buzz off. They wouldn't necessarily have to land and inject a toxin.
We live in interesting times.