By Lidia Kelly

MOSCOW/WARSAW (Reuters) - Russia summoned Poland's ambassador on Thursday to protest at the removal of a Soviet-era statue in a Polish town on the 76th anniversary of the Soviet invasion of Poland, highlighting increased tensions between the neighbors.

Katarzyna Pelczynska-Nalecz, Warsaw's envoy in Moscow, was called to the Russian Foreign Ministry to explain the dismantling on Thursday of a statue of Soviet General Ivan Chernyakhovsky in the Polish town of Pieniezno.

Chernyakhovsky was the youngest ever general in the Red Army and a decorated commander in its massive westward advance on Nazi Germany that helped end World War Two. He was killed in action at age 38 in February 1945.

Pelczynska-Nalecz said after the meeting that the Russian side objected to the statue's removal and asked for the process to stop. "I listened to it, I presented the Polish position on the issue that the whole process is 100 percent according to Polish law," Pelczynska-Nalecz told journalists.

Poland and Russia share a complicated history spanning war and peace. Following a pact with Nazi Germany, Stalin invaded eastern Poland in September 1939 soon after Adolf Hitler's forces invaded from the west.

The Red Army later freed Poland from Nazi occupation, but at the same time persecuted soldiers of the Polish underground army. After World War Two, Poland spent four decades under Soviet domination.

Chernyakhovsky was among those responsible for disarming and arresting thousands of Polish underground army soldiers towards the end of the war, many of whom were sent to Soviet prisons or labor camps, and died there. This earned Chernyakhovsky the nickname "executioner" in some parts of Poland.

Following communism's collapse, Poland embraced democracy and joined the European Union, and has recently been among the fiercest critics of Russia's annexation of Ukraine's Crimea.

Moscow's embassy in Warsaw issued a statement saying it had warned Poland many times that taking down Soviet-era monuments violated a bilateral agreement on protecting such sites and threatened the "most delicate feelings" of the Russian people.

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"(The actions) cannot be left without the most serious consequences for Russian-Polish relations," it said.

Poland says it observes the 1994 bilateral agreement and that it only applies to cemeteries. Russia says it concerns all war memorials.

Russian Foreign Ministry spokeswoman Maria Zakharova criticized Warsaw during a news conference. "Remembering history is what differentiates humans from animals," she said.

(Additional reporting by Gabriela Baczynska, Marcin Goettig and Agnieszka Barteczko in Warsaw; Writing by Lidia Kelly; Editing by Mark Heinrich)