Social networking company Facebook and search engine giant Google are considering a joint-venture with Skype after the latter delayed its initial public offering, two sources with direct knowledge of the discussions told Reuters.

It was reported that Facebook CEO Mark Zuckerberg has been involved in internal discussions about buying Skype, according to one of the sources. Meantime, the other source said that Facebook had reached out to the Luxembourg-based company about forming a joint venture.

Google has also held early talks for a joint venture with Skype, the second source said.

A Skype deal could be valued at $3 billion to $4 billion, the first source said. Skype's IPO is expected to raise about $1 billion, several other sources said.

The discussions are in early stages, and it is not clear which option the companies favor, the first two sources said.