Egyptian security forces are on high alert, with thousands of people expected to join anti-government rallies after Friday prayers.

本周五祈祷活动结束后，数以千计的埃及民众可能将加入反政府集会，保安部队目前正保持高度警惕状态。

The government says it is open to dialogue but also warned of "decisive measures" as the fourth day of violent protests loomed¹.

Widespread disruption（破坏，毁坏） has been reported to the internet and mobile phone messaging services.

There are also reports of arrests of opposition² figures overnight.

The reported crackdown on the largest opposition movement, the Muslim Brotherhood³, came after it said it would back the Friday protests.

On Thursday, Egyptian opposition figure and Nobel laureate（桂冠诗人，得奖者） Mohamed ElBaradei returned to Cairo, promising⁴ to join the street protests.

At least seven people have died since the protests began on Tuesday. They follow the so-called "Jasmine Revolution" in Tunisia, which saw President Zine al-Abidine Ben Ali flee into exile.

'Security sweeps'

Friday's rallies in Egypt are expected to be the biggest so far, with people being urged via internet sites to join the protests after attending prayers.

The protest organisers have called on people to come out in force, stressing that the religion of protesters is not relevant.

Late on Thursday, the Facebook and Twitter social websites had been disrupted along with mobile phone messaging, followed by loss of many internet services.

One internet user in Cairo, who wanted to remain anonymous⁵, told the BBC the 3G was not working and SMS messages were not being received.

He said: "Tomorrow's protest may exceed Tuesday's numbers, and I think tension will be high. People are trying to stay safe and are moving around in groups."

Associated Press news agency reported that the elite⁶ special operations counterterrorism force, which is rarely seen on the streets, had been deployed⁷ to key locations in Cairo, including Tahrir Square, where earlier protests have been held.

Egypt's interior ministry⁸ has warned it will take "decisive measures" against the protesters.

A lawyer for the Muslim Brotherhood told the BBC that tens of its members had been arrested.

Reuters news agency quoted a security source as confirming the authorities had ordered a crackdown. The source was quoted as saying: "We have orders for security sweeps of the Brotherhood."

Despite an official ban, the Muslim Brotherhood remains⁹ Egypt's largest and most organised opposition movement.

BBC Middle East editor, Jeremy Bowen, in Cairo, says political sources are saying that President Hosni Mubarak's security chiefs are telling him they can handle any trouble.

Mr Mubarak, 82, has not been seen in public since the protests began on Tuesday.

The Egyptian government tolerates（忍受） little dissent¹⁰ and opposition demonstrations¹¹ are routinely outlawed¹².

On Thursday, Mr Mubarak's ruling National Democratic Party said it was ready for dialogue, but did not offer any concessions¹³（让步，优惠） .

Safwat el-Sherif, the party's secretary general, said: "The NDP is ready for a dialogue with the public, youth and legal parties. But democracy has its rules and process. The minority does not force its will on the majority."

He also warned protesters to remain peaceful.

"I hope that all preachers at Friday prayers tomorrow are calling people to be peaceful in a clear, ritual（仪式的） way that never plays upon people's feelings to achieve an undesirable¹⁴ target."