World leaders are sending in their congratulations to U.S. President Barack Obama, who won a second term Tuesday in a tightly contested race with Republican challenger Mitt Romney.

U.N. Secretary-General Ban Ki-moon said he “warmly congratulates” Mr. Obama and looks forward to continuing to work together “in the spirit of the enduring partnership between the United States and the United Nations.” He noted some of the challenges that lie ahead — including ending the bloodshed in war-torn Syria.

Israeli Prime Minister Benjamin Netanyahu said that the strategic alliance between Israel and the United States is stronger than ever and that he will continue to work with President Obama. Mr. Netanyahu is a longtime friend of Mr. Romney, the president's challenger.

Russian President Vladimir Putin sent a telegram to Mr. Obama with his congratulations, while Mr. Putin's spokesman said Mr. Putin received the news “very positively.”

British Prime Minister David Cameron tweeted his “warm congratulations” publicly and said he looks forward to continued work together. But in a visit to Jordan Wednesday, Mr. Cameron told reporters that Mr. Obama needs to do more to help end the Syrian civil war.

The leaders of Kenya, home of Mr. Obama's father, both praised the president's re-election. President Mwai Kibaki said it is confirmation of the American people's confidence in their leader. Prime Minister Raila Odinga said the election result will re-ignite faith in democracy worldwide, but especially in Africa.

Mr. Obama's paternal grandmother lives in the Kenyan village of Kogelo, where she and other villagers celebrated the election's outcome. She told reporters she believes her grandson was re-elected because he has the capacity to love other people. And, as any grandmother ask of her grandson, she implored Mr. Obama to do his best at his job.