Talking to Aljazeera, Shaikh Ahmad Abd Al-Ghafur al-Samarai - a member of AMS, Iraq's highest Sunni authority - said he received a phone call to that effect.
On Monday morning, US forces in Humvees surrounded the mosque closing all roads leading to it, he said.
Shaikh al-Samarai said he received more information from one of the mosque's guards, who said five US Humvees surrounded the area preventing anyone from entering or exiting the mosque.
US forces said they had orders to search the whole area, including the mosque, as they had come under several attacks originating from the area, al-Samarai said quoting the guard.
Al-Samarai said he had no doubt the US forces had "bad intentions" and pre-scheduled plans.
"They [US forces] know that Um al-Qura mosque only hosts the AMS, which always calls on people to be reasonable and not escalate the situation," he said.
"The forces are still based there, searching anyone who walks in the street and have completely sealed the mosque"
Shaikh Ahmad Abd Al-Ghafur
al-Samarai, Association of Muslim Scholars member
"But at the same time, the AMS rejects the occupation and encourages Iraqis who want to overthrow it," he said. "The AMS is the most-influential Sunni authority in Iraq.
"The forces are still based there, searching anyone who walks in the street and have completely sealed the mosque," he added.
Meanwhile, a top aide of Shia leader Muqtada al-Sadr on Monday called on Shia parties participating in Iraq's National Conference to quit it.
"Shia parties like the Dawa party and the Supreme Council for Revolution in Iraq should quit the national conference," Shaikh Ahmad al-Shaibani said by telephone from Najaf.
The national conference is currently under way in Baghdad. The government had invited al-Sadr to attend, but he declined.
Early on Monday, several explosions were heard in Baghdad, but they did not appear to come from near the venue where Iraqi leaders are meeting.