Violent clashes have erupted between security forces and demonstrators in several Arab countries in the wake of Egypt's uprising.
In Bahrain - home to the United States' Middle East fleet - the main Shia opposition group has rejected King Hamad's offer of national dialogue to end days of unrest in the Gulf state.
Senior members of the Wefaq bloc said the government must resign first and troops should be withdrawn from the streets of the capital Manama.
The crisis has killed at least four people and wounded hundreds, with more than 60 hospitalised after Bahraini security forces fired on protesters in Manama.
The shootings occurred on a day of mass mourning for four people killed a day earlier when the police raided a protesters' camp in Pearl Square, wounding more than 200.
Soldiers in tanks and armoured vehicles have now taken control of the square, which the mainly Shi'ite protesters had hoped to use as a base like Cairo's Tahrir Square, the heart of protests that toppled the Egyptian President Hosni Mubarak nine days ago.
Violent protests spread
In Yemen, at least five people died when security forces and pro-government loyalists clashed with crowds demanding an end to the 32-year rule of President Ali Abdullah Saleh.
Medical officials and witnesses say two people were killed by gunfire in Aden as police moved to disperse protesters, while one person was killed in Taiz when a grenade was thrown from a car into a crowd of protesters.
In the Jordanian capital Amman, at least eight people are reported to have been injured after government supporters clashed with young protesters.
In the Red Sea city state of Djibouti, thousands have marched, calling for a change in government.
Obama calls for restraint
United States President Barack Obama has urged the governments of Bahrain, Libya and Yemen to show restraint in dealing with the protests, the reports of which he says have deeply concerned him.
Mr Obama has spoken with King Hamad bin Isa al-Khalifa of Bahrain, condemning the violence against peaceful protesters.
The US is facing a now familiar dilemma, torn between its desire for stability in a long-standing Arab ally and a need to uphold its own principles about the right of people to demonstrate for democratic change.