Iran has further restricted access to the Internet and blocked popular email services for the past few days, in a move a top lawmaker said could "cost the regime dearly," media reports said on Sunday.

Millions of Iranians have been unable to log onto their accounts on popular email websites such as Google's Gmail, Yahoo's Mail and Microsoft's Hotmail since Thursday without any official explanation, the Arman newspaper reported.

But the Mehr news agency said the restrictions were not related only to email.

"It has been a while that Internet users have had difficulty accessing domestic and news websites as well as foreign search engines and email services," it said on its website.

These difficulties include "low speed, outage and blocking" of websites, Mehr said.

A top conservative lawmaker, Ahmad Tavakoli, criticised the new "annoying" filtering and said it should be explained.

"The new filtering measure and cutting of access to the services used by most people without prior notice... will raise the ire of educated" people, he told Mehr.

"Such annoying filtering will cost the regime dearly."

Control over the flow of information is a key issue for Iran -- home to most Internet users in the Middle East with more than 36 million people out of the 75-million populace online.

Access to many globally popular websites, including Facebook, Twitter and YouTube, is blocked in the Islamic republic.

Iran in early 2011 launched a special police unit to combat "cyber crimes," especially those committed on social networking sites which are popular among the opposition and dissidents.

The Internet played a major role in the wave of anti-government protest that rocked the country after the disputed re-election of President Mahmoud Ahmadinejad in 2009.

Tehran also blocks most foreign news websites, accusing the Western media of taking part in a plot against it by the United States, Israel and Britain-led Europe.