Multiple videos posted on YouTube and appearing in Russian-language media today apparently depict militants firing Grad rockets into Ukraine from Russian territory.

Grads are Soviet-developed rockets sometimes fired from a truck-mounted missile battery. They can carry warheads weighing up to nearly 40 pounds a distance of up to 13 miles, although next-generation grads can travel nearly 25 miles.

Pro-Russian separatists in eastern Ukraine have already used shoulder-fired rocket launchers to bring down Ukrainian government aircraft. Now, militants have shown a willingness to use Russian territory as cover for potentially sophisticated long-range attacks on targets inside Ukraine.

Two videos depict a grad bombardment that the website The Interpreter geo-located within a Russian town near the Ukrainian border. In one, dozens of rockets streak into the sky in rapid succession. The other offers a clear view of what appears to be a second rocket volley:

The videos raises the possibility that Russia is allowing pro-Moscow separatists to attack Ukrainian government positions from inside its territory. This would remove almost all of the Kremlin's deniability surrounding its support for anti-Kiev militants in Ukraine's restive east. While Moscow's facilitation of anti-Kiev militant activity in Ukraine has been widely proven, the use of a complex heavy weapons system near one of the world's tensest borders would offer particularly stark proof of official Russian involvement.

The attacks would come within the context of increasing tension around the Ukraine issue. Kiev's uniformed military has made several gains in recent weeks, retaking major cities from pro-Russian militias. And today, the U.S. Treasury Department announced additional sanctions on Russian companies — wasting little time to increase pressure on Russian president Vladimir Putin after a missile allegedly fired from Russia brought down yet another Ukrainian aircraft.

This grad attack would be the latest escalation in a situation that's still far from resolved.