Several rockets struck Afghanistan’s capital of Kabul on Tuesday, shaking the main diplomatic district and sending foreign embassies into lockdown, officials and sources said.

It was not immediately clear if there were casualties or who was behind the attack on Afghanistan’s independence day at a time when the United States is withdrawing troops and encouraging peace talks to end almost 19 years of war.

“Several rockets were fired from two vehicles,” said Tariq Arian, an interior ministry spokesman.

Sources told Reuters the diplomatic area was quickly placed under lockdown after the blasts, as workers in embassies took cover in safe rooms.

Smoke billowed, alarms shrilled and shrapnel flew, said Reuters witnesses who heard at least four rockets landing near the Green Zone area, home to many foreign embassies and NATO headquarters.

“The warning alarm sounded two to three seconds before impact and then there was the sound of the first rocket, then, soon afterwards, another much louder one with a huge boom and shrapnel and bits of concrete fell,” added one of them.

A diplomatic source told Reuters one rocket had landed near a mosque just outside the tightly-guarded diplomatic enclave.

“All diplomatic officials in embassies in the green zone have been moved to safe rooms in the diplomatic district until clearance orders,” a senior Western security official added.

Teams were working to establish exactly where the rockets hit and if there were any casualties, an Afghan security official said.