The campaign of Barack Obama says the Democratic presidential hopeful is about to choose a running mate and wants his supporters to be the first to know.

Campaign manager David Plouffe has notified backers that they can sign up to receive an e-mail or text message "the moment" the decision is made.

The Obama campaign has used technology, especially the Internet, to build an on-line community of two million volunteers and to raise hundreds of millions of dollars in campaign funds.

Obama is vacationing in the U.S. Pacific state of Hawaii, two weeks ahead of the Democratic National Convention, where he and his vice presidential running mate will be formally nominated.

Republican presidential candidate John McCain campaigns Tuesday in Pennsylvania and New Jersey.  The veteran Arizona lawmaker is to be nominated as his party's candidate in the first week of September at the Republican National Convention. 

Some information for this report was provided by AFP and AP.