SAN FRANCISCO (Reuters) - Facebook Inc's recently acquired photo-sharing service Instagram removed a key element of its integration with Twitter, signaling a deepening rift between two of the Web's dominant social media companies.

Instagram Chief Executive Kevin Systrom said Wednesday his company turned off support for Twitter "cards" in order to drive Twitter users to Instagram's own website. Twitter "cards" are a feature that allows multimedia content like YouTube videos and Instagram photos to be embedded and viewed directly within a Twitter message.

The move marked the latest clash between Facebook and Twitter since April, when Facebook, the world's no. 1 social network, outbid Twitter to nab fast-growing Instagram in a cash-and-stock deal valued at the time at $1 billion. The acquisition closed in September for roughly $715 million, reflecting Facebook's recent stock drop.

The companies' ties have been strained since. In July, Twitter blocked Instagram from using its data to help new Instagram users find friends.

Beginning earlier this week, Twitter's users began to complain in public messages that Instagram photos did not seem to display properly on Twitter's website.

Systrom confirmed Wednesday that his company had decided its users should view photos on Instagram's own Web pages and took steps to change its policies.

"We believe the best experience is for us to link back to where the content lives," Systrom said in a statement, citing recent improvements to Instagram's website.

"A handful of months ago, we supported Twitter cards because we had a minimal Web presence," Systrom said, noting that the company has since released new features that allow users to comment about and "like" photos directly on Instagram's website.

The move escalates a rivalry in the fast-growing social networking sector, where the biggest players have sought to wall off access to content from rival services and to their ranks of users.

"They're both competing for slices of the same pie, the pie being users' attention," said Ray Valdes, an analyst with research firm Gartner.

If Facebook decides to offer advertising on Instagram, it's important that the users visit Instagram's own website, said Valdes. "If the eyeballs are elsewhere, you have less to work with in terms of monetization," he said.

Photos are among the most popular features on both Facebook and Twitter, and Instagram's meteoric rise in recent years has further proved how picture-sharing has become a key front in the battle for social Internet supremacy.

Instagram, which has 100 million users, allows consumers to tweak the photos they take on their smartphones and share the images with friends, a feature that Twitter has reportedly also begun to develop. Twitter's executive chairman, Jack Dorsey, was an early investor in Instagram and had hoped to acquire it before Facebook CEO Mark Zuckerberg made a successful bid.

When Zuckerberg announced the acquisition in an April blog post, he highlighted Instagram's inter-connectivity with other social networks.

"We think the fact that Instagram is connected to other services beyond Facebook is an important part of the experience," Zuckerberg wrote. "We plan on keeping features like the ability to post to other social networks."

A Twitter spokesman declined comment Wednesday, but a status message on Twitter's website confirmed that users are "experiencing issues," such as "cropped images" when viewing Instagram photos on Twitter.

(Reporting By Alexei Oreskovic and Gerry Shih; Editing by Nick Zieminski and Leslie Adler)

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