(Reuters) -Commercial airlines around the world on Monday were weighing how long to suspend Middle East flights after the U.S. struck Iran.

Singapore Airlines, one of the highest-profile in Asia, had called the situation "fluid" on Sunday as it cancelled flights from Singapore to Dubai following a security assessment.

The Middle East route has become more important for flights between Europe and Asia since Russian and Ukrainian airspace closed due to war, but flight tracking website FlightRadar24 showed empty space over Iran, Iraq, Syria and Israel.

Air France KLM said on Sunday that it cancelled flights to and from Dubai and Riyadh on Sunday and Monday. British Airways, owned by IAG ICAG.L, also cancelled flights to and from Dubai and Doha for Sunday. It was still reviewing the situation, it said in a statement on Sunday evening, when asked about later flights.

Missile and drone barrages in a growing number of conflict zones represent a high risk to airline traffic, and an organization that monitors flight risks, Safe Airspace, a website run by OPSGROUP, warned on Sunday that U.S. attacks on Iran's nuclear sites could heighten the threat to American operators in the region. 

In the days before the U.S. strikes, American Airlines ( AAL ) suspended flights to Qatar and United Airlines did the same with flights to Dubai.

Airlines are also concerned about a potential spike in oil prices following the U.S. attacks, which will increase the cost of jet fuel. [O/R]    

Israel meanwhile is ramping up flights to help stranded travellers at home and abroad. The country's Airports Authority says that so-called rescue flights to the country would expand on Monday with 24 a day, although each flight would be limited to 50 passengers. Israeli airline El Al on Sunday said it had received applications to leave the country from about 25,000 people in about a day.