Egyptian protesters have torched a police station in Port Said as US Secretary of State John Kerry landed in Cairo to push for political leaders to reach a consensus following contested elections.
A 500-strong mob threw stones and petrol bombs, setting the police station on fire before blocking fire engines from approaching the blaze, the interior ministry said. Witnesses said police used tear gas and plastic bullets to subdue protesters.
The protests began outside the station after two men were injured when a police truck hit them during earlier clashes in the city, where a general strike has now entered its third week.
Meanwhile, one person was killed and dozens injured in overnight clashes between police and protesters in Mansoura, in the Nile Delta, according to security officials.
Clashes have erupted across the country as the stalemate between Islamist President Mohamed Morsi and the secular-leaning opposition drags on. The opposition has ratcheted up the pressure on the president by declaring a boycott of next month's election.
Opposition leaders including former International Atomic Energy Agency chief Mohamed ElBaradei rejected invitations to meet Kerry, and condemned the US stance of opposing their electoral boycott.
National Salvation Front leader Hamdeen Sabahi said he and ElBaradei rejected Washington's call to reconsider its boycott, and had turned down invitations to meet Kerry in Cairo.
"I received an invitation and turned it down, and Dr ElBaradei received an invitation and he turned it down," Sabahi told ONTV. "We want to send a message that we reject American pressure."
An aide to Egypt's former foreign minister Amr Mussa, another NSF leader, said Mussa also refused to meet Kerry, but would send a lower-ranking representative in his place.
"We see there is no way we can participate in the election," said the aide. "This is an NSF decision, and the unity of the NSF is our number one priority."
US State Department spokesman Patrick Ventrell said: "The secretary is looking forward to his visit to Cairo to see what we can do to help the Egyptian people in terms of their democratic aspirations and looking at some of the economic challenges they have. We're a friend of the Egyptian people, and he looks forward to meeting a variety of Egyptian interlocutors from a variety of walks of life."
The NSF had demanded guarantees of electoral transparency as a condition for their participation, and has criticised US support for Morsi.
A number of NSF members backed Morsi in last June's election against Ahmed Shafiq, the last prime minister to serve under ousted leader Hosni Mubarak. But they now accuse Morsi of betraying the democratic uprising which overthrew Mubarak in early 2011, and sidelining liberals and Christians.
In a phone call to Morsi last week, US President Barack Obama welcomed the Egyptian president's commitment to represent all Egyptians, but encouraged him to find common ground with the opposition.
US officials said Kerry would be pressing Egypt to adopt the reforms necessary to qualify for a $4.5bn International Monetary Fund loan package.