Sen. Barack Obama is canceling presidential campaign events Thursday and Friday so that he can visit his gravely ill, 85-year-old grandmother in Hawaii.

Campaign spokesman Robert Gibbs told reporters Monday night that events in Iowa and Wisconsin have been canceled and that Sen. Obama will leave for Hawaii on Thursday afternoon after an event in Indianapolis.

“Sen. Obama’s grandmother, Madelyn Dunham, has always been one of the most important people in his life, along with his mother and his grandfather,” Gibbs said.

Dunham, who helped raise Sen. Obama, was released from the hospital late last week, but Gibbs said her health had deteriorated “to the point where her situation is very serious.” Dunham turns 86 on Sunday.

Obama recognized his grandmother in his nomination acceptance speech at the Democratic National Convention. He said she taught him about hard work and that she was the one “who put off buying a new car or a new dress for herself” so he could have a better life.

Earlier in his campaign, Obama mentioned his grandmother in a speech he made in March defending his past association with his former pastor Jeremiah Wright, who came under fire for his racially charged sermons.

In that speech Obama, whose mother was white and father black, said he could “no more disown [Wright] than I can my white grandmother - a woman who helped raise me, a woman who sacrificed again and again for me, a woman who loves me as much as she loves anything in this world, but a woman who once confessed her fear of black men who passed her by on the street, and who on more than one occasion has uttered racial or ethnic stereotypes that made me cringe.”

The schedule switch means Obama will miss events Thursday in Des Moines, Iowa, and Madison, Wis. On Friday, Michelle Obama will stand in for her husband at rallies in Ohio.

Meanwhile, Sen. John McCain was spending Tuesday in the battleground state of Pennsylvania before heading Wednesday into New Hampshire, where this year the race is competitive.