(CNN) The United Arab Emirates on Tuesday resumed its participation in airstrikes against ISIS, the country said -- its first publicly known foray against the terror group since it reportedly suspended attacks over concerns about pilot safety.

UAE F-16s stationed in Jordan took part in morning attacks and returned safely to base, the UAE military said without saying where the strikes happened.

A U.S.-led coalition has been conducting airstrikes against ISIS in Syria and Iraq, where the Sunni Muslim extremist group has captured territory for what it calls its Islamic caliphate.

The UAE halted its participation in the strikes in December because leaders were worried there were insufficient plans to save personnel who may be captured, a senior U.S. military official told CNN.

The safety issue was highlighted by the case of Jordanian military pilot Lt. Moath al-Kasasbeh, whom ISIS captured in December after his jet crashed in Syria . Last week, ISIS released a video showing its fighters burning al-Kasasbeh to death.

A representative of the UAE government told CNN that no comment would be offered about the airstrike suspension.

ISIS declared it had established a caliphate spanning Iraq and Syria last year. Since then, it has gone on a murderous rampage that has included beheadings of foreigners.

There are about 20,000 fighters in Syria who belong to terror groups such as ISIS, the director of the National Counterterrorism Center will tell a House committee on Wednesday, according to remarks obtained by CNN.

"The United States and our allies are increasingly concerned with the more than 20,000 foreign fighters who have traveled to Syria from over 90 different countries," Nick Rasmussen plans to tell the Homeland Security Committee. That is 1,000 higher than the number of foreign fighters in an estimate given by intelligence officials in January.

The numbers of Westerners -- 3,400 -- and Americans -- 150 -- who have gone to Syria are similar to numbers given by officials in recent months.

Hundreds of thousands of Iraqis and Syrians have fled areas ISIS has seized. The United States, along with European and Arab nations, began airstrikes against the terror group last summer.

Kurds take bridgeheads near Mosul

Kurdish fighters have captured three important bridgeheads on the Tigris River near the northern Iraqi city of Mosul, developments that further restricts ISIS' movement outside Iraq's second-largest municipality, U.S. military and Kurdish officials said Tuesday.

ISIS took control of Mosul in June. But Kurdish ground forces, as well as airstrikes from the U.S.-led coalition, recently have tried to cut off Mosul's lines of supply to ISIS in Syria, setting up what could be an eventual assault by the Iraqi military later this year to expel the terror group from the city.

The three captured bridgeheads are on the west bank of the Tigris north of Mosul, U.S. Central Command and Kurdish officials said.

Besides hindering ISIS' movement outside the city, the Kurds' gains would protect key points through which an operation to liberate Mosul could take place.

Mosul is a predominantly Arab city, though the Kurds have an autonomous region to the north and east. Few expect the Kurds to be involved in clearing Mosul of ISIS -- that would be a job for Iraqi government security forces.

But with Mosul so close to their territory, the Kurds do have an interest in choking off ISIS and preventing them from advancing.

Iraqi ground forces could begin a move to retake the city as soon as April, a U.S. Central Command official told CNN last week.

Tuesday's developments come three days after heavy coalition airstrikes around Mosul -- part of what Kurdish fighters said was the heaviest day of bombardment they had witnessed there.