They were received by Muslim families in East London and the Midlands last week, believed due to the imagery on it to have been sent by the mysterious "Last Soldiers of Christ' group".
"This is further to the two items investigated yesterday, both of which were found to be non-harmful", the spokesman said.
The packages were accompanied with offensive letters, the MPs said.
Police are investigating another suspicious package sent to MPs' offices in Westminster, the fourth in recent days.
All four packages have been found in the Norman Shaw north building in Westminster, which houses MPs' offices and is linked by a walkway to Portcullis House.
'We assessed two people at the scene and took them to hospital'.
Parliament has received four such packages over the past 24 hours, police told Business Insider.
A mysterious liquid was discovered in Mohammad Yasin's parliamentary office this lunchtime, according to sources.
Rashford insists he doesn't need Mourinho reassurances
De Gea meanwhile has played 3,150 minutes this season and another 3,420 but he is the no.1 keeper after all. "But Mourinho is not like that.
All three packages contained letters advertising "Punish A Muslim Day", which listed Islamophobic actions and the number of points given for performing them.
It is also said to include pointers for bombing or burning down a mosque.
"We are aware of a potential situation involving a suspicious substance which the Met Police are investigating", a parliamentary spokesperson said.
A spokesperson for Scotland Yard said: 'Police were called at 12.58pm on Monday, 12 March to reports of a suspicious package at Norman Shaw Buildings, Victoria Embankment, Westminster.
"The London Ambulance Service are on scene".
Two people have been taken to hospital as a precaution after the package was reportedly sent to Labour's Mohammed Yasin, the MP for Bedford.
Her staff said they were "thrown into a panic" by security after the incident, but the Home Secretary was out of the country.