|Protesters have clashed with police in riots over allegations of election fraud [Reuters]
The United States has said reports of irregularities in Egypt's parliamentary elections raises questions about the "fairness and transparency" of the process.
The state department said it had closely followed the Sunday's polling and that reports from civil society monitors, candidate representatives, and government officials on the conduct of Sunday's elections gave "cause for concern".
"We are disappointed by reports in the pre-election period of disruption of campaign activities of opposition candidates and arrests of their supporters, as well as denial of access to the media for some opposition voices," PJ Crowley, the state department spokesman said in a statement on Monday.
"We are also dismayed by reports of election-day interference and intimidation by security forces."
Egypt has already rejected US criticism of its refusal to allow foreign monitors to observe the polls, accusing Washington of interfering in its internal affairs.
Egypt is a key US ally in the Middle East and receives billions of dollars a year in US assistance.
It is also a major player in the now-stalled peace negotiations between Israel and the Palestinians, an important foreign policy initiative for President Barack Obama who delivered a major speech on US relations with the Muslim world in Cairo last year.
Earlier on Monday, protesters set fire to cars, tires and two polling stations and clashed with police in riots over allegations that Egypt's ruling party committed widespread fraud to sweep the elections.
Rights groups, which monitored the poll, backed up opposition complaints that it had been marred by fraud and violence but the government insisted it had been conducted fairly.
Official results are due out on Tuesday.
Egypt's main opposition party, the Muslim Brotherhood, said that it had lost most of its seats in parliament in an election it charged had been "rigged and invalid".
Analysts previously said the government would seek to move its most vocal critic in parliament to the sidelines of official politics as it prepares for a presidential election in 2011.
Officials have indicated Mubarak, in power since 1981, and whose health has been under renewed scrutiny since gallbladder surgery in March, will seek a new term if able. If not, many Egyptians think his son, a top party official, will stand.