KABUL, June 6 (Xinhua) -- A rocket fired by militants struck the center of Afghanistan's capital of Kabul Tuesday morning when an international conference of peace and security cooperation was going on, sources and local media said.

"The rocket struck an empty sport ground in Shash Darak locality in Police District 9 at around 11:25 a.m. local time and the blast did not cause any casualties," a source told Xinhua anonymously.

Several diplomatic offices and apartment buildings are located in the area, where the headquarters of NATO-led Resolute Support also located.

The source said details about the incident will be shared later on the day.

Earlier on Tuesday, an international conference titled "Kabul Process" with the participation of 20 countries and international organizations, including the United States, Russia, China, the United Nations, NATO and the European Union opened in Kabul amid tight security.

No group has claimed responsibility for the attack so far.

Kabul has been the scene of a series of attacks recently.

On Wednesday, a massive truck bombing struck the nearby diplomatic Wazir Akbar Khan district, killing 150 people and injuring 450 others.

The Afghan government has beefed up security measures ahead of the conference and blocked all the streets leading to the venue of meeting.