A pro-Russian separatist casts a ballot during the self-proclaimed Donetsk People's Republic leadership and local parliamentary elections at a polling station in Novoazovsk on Sept. 2. (Maxim Zmeyev/Reuters)

Ukraine’s president, Petro Poroshenko, warned Monday that he might scrap portions of a cease-fire deal in response to rebel-held elections in the east. The announcement came as international observers said a drone flying above the region as part of a truce-monitoring mission had been fired upon.

Poroshenko said he would convene his security advisers Tuesday to discuss the elections held Sunday by pro-Russian rebels who have taken over territory in eastern Ukraine. The vote was praised Monday by Russia but condemned by the United States, the European Union and the United Nations.

In a nationally televised speech, the Ukrainian president said he may move to revoke a law that granted extensive autonomy to separatist-held territory. Sunday’s elections, he said, “sharply aggravated” the situation in the east. Poroshenko said, however, that he would propose another self-rule law if the rebels and Russia live up to their side of the peace agreement, which envisions the separatists handing over control of areas along the Ukraine-Russia border to the central government in Kiev.

The drone came under attack during the elections, a spokesman for the Organization for Security and Cooperation in Europe (OSCE), Michael Bociurkiw, said Monday.

Unmanned aerial vehicles have been patrolling the skies of eastern Ukraine since Oct. 23 to help monitor the cease-fire, which has been routinely violated since going into effect about two months ago.

Separatist leader Alexander Zacharchenko sweeps polls in rebel-held eastern Ukraine to become the head of the Donetsk People’s Republic, a breakaway region. (Reuters)

The OSCE said a man in camouflage near a checkpoint spotted the drone Sunday afternoon and pointed a shoulder-fired missile at it. Then he put down the weapon and yanked a tarp off the back of a civilian truck to reveal an antiaircraft gun mounted on the vehicle. He immediately fired “numerous” rounds at the drone, although the aircraft was not hit and later landed safely, the OSCE said in a statement.

The OSCE did not specify whether the shooter was a rebel, but it said the incident occurred in separatist-held territory, near the coastal village of Shyrokyne, about 12 miles east of the government-held city of Mariupol.

Shoulder-fired missiles were used to bring down several Ukrainian military planes in the early months of the conflict. At the time, rebels said they had captured the weapons from Ukrainian military depots. The Ukrainian military accused Russia of supplying the rebels with the weapons, a claim that Russia denied.

The cease-fire war in Donetsk

Bociurkiw said four drones are now deployed in eastern Ukraine, giving the OSCE the ability to conduct round-the-clock surveillance, weather permitting. Sunday’s incident was the second involving a drone, he said. The first occurred Wednesday, when a drone was “subject to GPS jamming or scrambling,” Bociurkiw said. The OSCE is investigating that incident.