WARSAW, Poland - President Obama on Friday honored the memories of those slain in the Warsaw Ghetto uprising against Nazis, telling one elderly man that the memorial was a "reminder of the nightmare" of the Holocaust in which six millions Jews were killed.

The president placed a wreath at the Tomb of the Unknown Soldier, dedicated to all unidentified soldiers who have given their lives for Poland in past wars.

The American president's homage to Poles who fell in World War II, at two symbolically potent sites, was sure to carry great weight in a country whose identity is still profoundly shaped by the death and destruction inflicted on it by Nazi Germany.

In the final phase of his European trip, Obama greeted Holocaust survivors and leaders of Poland's Jewish community at the Monument to the Ghetto Heroes. He smiled, shook hands, and hugged those gathered under a light rain, including some who shared memories of having met Obama at earlier times.

"What a wonderful visit. I'll have to bring my daughters," Obama said as he exited.

The monument in the former Jewish ghetto commemorates the tens of thousands of Jews killed in a 1943 uprising against the Nazis during Germany's occupation of Poland during World War II.

Most of the insurgents in that uprising were killed, but the event bears great importance in Jewish history as an example of Jews bravely taking up arms to defend themselves against the Nazis. It's also a key memorial in a country that before the Holocaust was home to Europe's largest Jewish community.

Among those Obama met was Halina Szpilman, widow of Wladyslaw Szpilman, the Holocaust survivor featured in Roman Polanski's film The Pianist.

A leading member of the Jewish community, Monika Krawczyk, urged Obama to do all he could to support Israel, saying, "It's the only Jewish state we have." He assured her the United States would be there for Israel.

Obama arrived in Warsaw hoping to inject new vigor into a relationship with an ally that has sometimes felt slighted.

At the Tomb of the Unknown Soldier, he chatted warmly with elderly veterans in uniform who had fought Nazi Germany, including at least one woman.

Hours before he arrived, Polish headlines were dominated by news that he was being snubbed by legendary Solidarity founder Lech Walesa, who said he was refusing to meet Obama.

"This time a meeting does not suit me," the 67-year-old former president said. Walesa refused to divulge more, but it seemed possible he was offended at not being offered a one-on-one meeting with Obama early on.