WASHINGTON - US President Barack Obama urged Americans to show generosity to Syrian refugees in his Thanksgiving message on Thursday, reminding them that the Pilgrims who came to America in 1620 were themselves fleeing persecution."Nearly four centuries after the Mayflower set sail, the world is still full of pilgrims - men and women who want nothing more than the chance for a safer, better future for themselves and their families," Obama said in his address.Obama's plan to accept 10,000 refugees from Syria became a lightning rod for political criticism after attacks, claimed by Islamic State militants, killed 130 people in Paris two weeks ago. The United States is leading an international coalition fighting the group in Syria and Iraq.Since the Paris attacks, Americans now identify terrorism as the most important problem facing the country, Reuters-Ipsos polling shows.The US House of Representatives passed a bill to suspend the refugee plan and intensify refugee screening measures before lawmakers left Washington for the Thanksgiving break. Several Republican candidates for the November 2016 presidential election have also said the refugees pose a risk."People should remember that no refugee can enter our borders until they undergo the highest security checks of anyone traveling to the United States," Obama said in his address.Obama has vowed to veto the House refugee bill. But the White House has said it is open to working with lawmakers on tighter security measures for visitors from 38 countries who do not need a visa for short visits to the United States.In his address, Obama quoted from letters he had received from Americans welcoming Syrian refugees."One woman from Pennsylvania wrote me to say, 'Money is tight for us in my household ... But I have a guest room. I have a pantry full of food. We can do this,'" Obama said."Another woman from Florida told me her family's history dates back to the Mayflower - and she said that welcoming others is part of 'what it means to be an American,'" he said.