Former U.S. President Barack Obama warned on Friday against rhetoric he said was designed to sow fear as he campaigned in support of Democratic candidates while President Donald Trump hammered a hard-line anti-immigration message to energize Republicans.

In a packed day of campaigning ahead of Tuesday's congressional midterm elections, Trump continued a blitz of rallies urging voters to keep his Republican Party in control of Congress, while Democrats appeared to notch a win in their efforts to halt the spread of misinformation online.

Twitter said it had deleted more than 10,000 automated accounts posting messages that discouraged people from voting in Tuesday's elections and wrongly appeared to be from Democrats, after the party flagged the misleading tweets to the social media company.