Commercial airlines around the world on Monday were weighing how long to suspend Middle East flights as a conflict which has already cut off major flight routes entered a new phase after the U.S. attacked key Iranian nuclear sites and Tehran vowed to defend itself.

Singapore Airlines said on Sunday it canceled two flights between Singapore and Dubai, warning in an advisory that other flights between the Southeast Asian country and the emirates may be affected.

"While there have been no specific threats made against civil aviation, Iran has previously warned it would retaliate by attacking US military interests in the Middle East – either directly or via proxies such as Hezbollah," Safe Airspace said.