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ARTEMIVSK, Ukraine — An explosion in downtown Kiev, Ukraine, on Friday injured at least two people and ignited fears of new conflict in the city, where protest barricades and tents still stand in the central square months after demonstrations that toppled the government.

Kiev’s deputy police chief said in a statement shortly after the blast that the police had arrested a man who had thrown a grenade toward a convention center. The motive for the attack was not immediately clear.

Clashes broke out the day before when municipal workers and national guard units tried to clear the square of holdout protesters from the February demonstrations that led to the ouster of the president, Viktor Yanukovych. The workers abandoned their attempt when a tent caught fire.

The continuing presence of protesters in the square, called the Maidan, has become a source of contention in Ukraine, as well as in neighboring Russia, where the square is often portrayed as a source of anti-Russian feeling and Ukrainian nationalism.

In the turbulent east of Ukraine, officials said that 15 soldiers had been killed and 79 injured in the last 24 hours in clashes with pro-Russia separatists, an unusually high number of casualties for a single day.

Andriy Lysenko, a military spokesman, said that the heavy losses came when a Ukrainian unit that had spent almost a month surrounded by rebel forces near the Russian border broke out of its encirclement.

Fighting also continued not far from the wreckage of the Malaysia Airlines flight that was shot down last month, killing all 298 people on board.

Lysenko on Thursday told journalists that separatist forces had been firing artillery from the site of the wreckage.

Military police officers and forensic experts from the Netherlands and Australia who had been gathering human remains left the Donetsk region Thursday because of shelling and gunfire near the crash site.

Also on Friday, Ukraine’s defense minister announced that several pilots had been wounded when their helicopter, which he said was used to carry injured soldiers, was shot down by rebel forces.

U.S. Ambassador Samantha Power delivered the warning at a United Nations Security Council meeting focusing on the human rights situation in Ukraine’s east. Recent reports by the West and the Kiev government have accused Moscow of dispatching what NATO estimates is 20,000 troops to the border.

Power said Russia has not only increased aid to the separatists but has amassed “more and more” troops and hardware near the border, began extensive military exercises this week and launched shells across the border into Ukraine.

The New York Times and the Associated Press contributed to this report.