'I'm at Twitter'

Medvedev began the day in San Francisco, where he sent his first microblog, or tweet, from the San Francisco offices of Twitter.

"Hello everyone, I'm at Twitter and sending my first message," he wrote in Russian. The short messages broadcast over the Internet have become one of the biggest new technology hits.

U.S. relations with Russia have warmed under President Barack Obama, who has tried to "reset" ties after tenser times under the previous administration.

But the United States still insists Russia must focus on improving protection of intellectual property if it wants to join the World Trade Organization, a subject Obama and Medvedev are expected to discuss later in the week in Washington.

"The Russians are going to have to take the practical steps that any other prospective member of the WTO needs to take," a senior administration official said on condition of anonymity.

"This isn't a favor to us or to the WTO. It's deeply in the self-interest of protecting the intellectual output, the innovation that comes out of Russian industry," the official added.

Medvedev's whirlwind itinerary also includes visits with Apple Inc (AAPL.O) chief Steve Jobs and Russian Web search firm Yandex, as well as delivering a speech at Stanford University.

Medvedev has described the Silicon Valley as a place to learn lessons about modernization.

"This experience is not definitive, but it is quite interesting," local press quoted him as saying before he left Russia. He has said he wants to build a high-tech hub outside Moscow with tax breaks and special rules.

Critics want rules that everyone can play by, though. One tech star born in Russia that Medvedev won't meet is Google Inc founder Sergey Brin, who once called Russia "Nigeria with snow."

Russia rated a 2.2 out of 10 in a measure of business confidence in the 2009 Corruption Perception Index from Transparency International - behind Nigeria. Its best score of the last decade, 2.8 in 2004, tied Russia with Tanzania and Mozambique.