Egypt's largest organized opposition group, the outlawed Muslim Brotherhood, says it will join major anti-government protests planned to take place after Friday prayers in the world's most populous Arab nation.
After days of official inaction, the group said on its website Thursday it would fully enter the demonstrations that have swept across the country for the past three days organized by smaller opposition groups calling for an end to President Hosni Mubarak's 30-year-old rule.
Five people have been killed in the unrest and the government said about 800 people have been detained since Tuesday. Human rights groups say there have been more than 2,000 arrests.
Earlier Thursday, Mohamed ElBaradei, the Nobel peace laureate and former head of the U.N. nuclear agency who has become a leading Egyptian reformer, returned to Cairo in an attempt to galvanize the youth-led protests. He warned Egypt's government against using violence against protesters.
In Washington, U.S. President Barack Obama said political reforms were "absolutely critical" to Egypt's "long-term well-being," boosting pressure on Mr. Mubarak to implement changes while acknowledging he is a critical U.S. ally.
In his first comments on the unrest in Egypt, Mr. Obama urged the government and the protesters to refrain from violence. The U.S. president, in an interview broadcast live on the YouTube website, said Mr. Mubarak has been "very helpful on a range of tough issues" but that his government must move forward on "political and economic reform."
Meanwhile, violence escalated in areas outside the Egyptian capital Thursday.
In the flashpoint city of Suez, east of the Egyptian capital, witnesses said rioters firebombed the main fire station and firefighters jumped out of windows to escape the flames. Police fired tear gas and rubber bullets at the protesters.
In the northern Sinai area of Sheik Zuweid, several hundred bedouins and police exchanged live gunfire, killing a 17-year-old man. Hundreds of protesters also clashed with police in the city of Ismailia.
Trading was halted briefly on Egypt's stock market on Thursday, and the key index fell another 11 percent - the sharpest drop in about two years, costing investors billions of dollars in market value and dropping the year-to-date loss to about 21 percent.
Earlier Thursday, ruling party secretary general Safwat El-Sherif said the government was open to public dialogue with the country's youth, who have fueled many of the protests over the past few days.
The April 6th Youth movement and other groups responsible for organizing the protests using social media websites such as Facebook and Twitter, say they speak for young Egyptians frustrated with the kind of poverty and oppression that triggered Tunisia's unrest, toppling that country's president earlier this month.
By Thursday evening, Facebook, Twitter and Blackberry Messenger services were reportedly interrupted, possibly a move by authorities to hamper protesters from organizing.
Slideshow of Egyptian protests
Some information for this report was provided by AP, AFP and Reuters.