UPDATE 2-Mousavi supporters rally support on Twitter
* Twitter messages rally support for opposition
* Websites are focal point for young Iranians
* U.S. State Dept. asked for Twitter outage delay
(adds State Dept. comment, paragraphs 5-7)
LONDON, June 16 (Reuters) - Supporters of defeated Iranian presidential candidate Mirhossein Mousavi posted defiant messages on Twitter on Tuesday, calling for a second banned pro-Mousavi rally to go ahead and offering security updates.
Social networking websites such as Twitter and Facebook have become a focal point for young, urban Iranians opposed to President Mahmoud Ahmadinejad, who defeated Mousavi in Friday's presidential election and whose government controls the state media.
"Alert: Mousavi march still on. 5PM," read one short message, or "tweet," on Twitter.
"Good luck at the march. Don't take cars, they will be waiting for you when you return to them," read another, as tweets on the subject of the Iranian election poured onto the site every few seconds.
A U.S. official said meanwhile that the U.S. State Department had contacted Twitter at the weekend to urge it to delay a planned upgrade that could have cut daytime service to Iranians.
"We highlighted to them that this was an important form of communication," the official said of the conversation the department had with Twitter. The official, speaking in Washington, declined further details. The request was made despite the Obama administration's stated concern not to meddle in the post-election dispute.
Twitter had said earlier it had delayed the upgrade, without mentioning any contact with the U.S. government.
BLOCKED TEXT MESSAGES
The Iranian government blocked SMS text messages during polling after opposition candidates used them to galvanise key young voters during the fiercely contested election campaign, and Tehran residents were still unable to send SMSs on Monday.
The BBC's Persian service was also blocked.
Social networking site Facebook, which has about 150,000 members in Iran, said on Monday it had had reports that some users in Iran were having difficulties accessing Facebook. Continued...
