Last year, he survived a campaign by Shia and Kurdish politicians to remove him after he said Iraqis who killed US troops should be celebrated as heroes.
Last month, he slapped a fellow Sunni politician in the face and called him "scum" at the end of a house session.
Omar said he was shoved by al-Mashhadani's security guards as the speaker made his way to the an Iraqi parliament chamber floor in the US-protected Green Zone in central Baghdad.
He said after being dragged to an unused office and locked in there, "al-Mashhadani came to me when his guards freed me and he apologised by saying that he did not recognise me".
Also on Monday, Gordon Brown, the Britain's next prime minister, made a surprise visit to Iraq for what he called a fact-finding trip to evaluate the UK's involvement in the war.
It is his first visit since being confirmed as the successor to Tony Blair, whose popularity at home waned over his support for the US-led war.
|Brown says he is is in Iraq |
to "listen and learn" [AFP]
Brown said he wanted to "listen and learn" before taking office on June 27.
The prime minister in-waiting said he was in Iraq to see the impact of al-Qaeda, Iran and "to see all the people on the ground and make an assessment of what's happening so I'm better informed".
Brown has said he will reduce troop numbers when possible, but aides say he is unlikely to make any big sudden shifts in policy as the British military is already planning further cutbacks.
Brown, who has repeatedly stressed that economic regeneration is vital to end the violence, said he would also talk to Nuri al-Maliki, the Iraqi prime minister, about the economy.
Brown's visit comes amid a sequence of bridge attacks in Iraq.
On Sunday evening, a suicide car bomb attack on a bridge south of Baghdad killed three US soldiers and wounded six more, a US said on Monday.
On Monday, a suicide car-bomber struck a major bridge in Iraq's volatile Diyala province, police said, cutting the crossing over the Diyala river.
Police said they did not know if there were any casualties. The bridge, normally guarded by Georgian troops, links the provincial capital Baquba with villages in the north of Diyala.