Twitter has fired the latest salvo in its social media war with Instagram by offering its own smartphone photo-sharing features.
It was forced to act after the Facebook-owned firm made it impossible for Internet users to integrate Instagram images into their tweets.
"Starting today, you'll be able to edit and refine photos, right from Twitter," wrote Coleen Baik, a senior designer with Twitter, in a blog post.
"Every day, millions of people come to Twitter to connect with the things they care about and find out what's happening around the world.
- Math, science scores for some US students improving, but lag behind many in Asia, Europe
- Indiana Jones and the mystery of the Belizean crystal skull
- Pope challenges Justin Bieber for Twitter supremacy
- Nazi Twitter account silenced in Germany
- 20 must-follow fake Twitter accounts
- 10 Celebrity Twitters of the Week
"As one of the most compelling forms of self-expression, photos have long been an important part of these experiences."
Twitter said its partner Aviary was powering filters and other effects for images using the latest Twitter applications for Apple iPhones or smartphones running on Google-backed Android software.
The feud between Twitter and Instagram escalated over the weekend when the smartphone photo-sharing service stopped internet users viewing its images in tweeted messages.
Instagram, which has some 100 million users, is seeking to route photo viewers to its own website instead. It then has potential to make money from adverts or other mechanisms, instead of letting Twitter get the benefits.
Previously, Instagram pictures shared in messages tweeted from smartphones could be viewed unaltered on Twitter.
Twitter confirmed on Sunday that Instagram had disabled its photo integration with Twitter, and photos were no longer appearing in tweets or user photo galleries.
Instagram rose to stardom with the help of Twitter, but has distanced itself from the messaging service since being acquired by Facebook.
Last month, Instagram was revamped with the roll-out of online profiles that let people showcase themselves and photos they have taken with the smartphone application.
People can share their profiles with whomever they wish, as well as "follow" other Instagram users, commenting on or expressing "likes" for pictures.
A distinctive feature of Instagram is that it allows users sharing smartphone snaps to enhance them with image filters for artistic effects such as mimicking historic types of film.