U.S. Secretary of State Hillary Clinton called on Russia and China Tuesday to be "part of the solution" to the crisis in Syria and warned that any hope for peace depended on a political transition.

"We believe there is a way forward and we are ready to pursue that. And we invite the Russians and the Chinese to be part of the solution," she said at a news conference in the Georgian Black Sea city.

Three leading Bahraini opposition activists, facing up to life in jail on charges of plotting to overthrow the monarchy, told their trial on Tuesday of how they were tortured in custody, their lawyers said.

The three - Shiite clerics Abduljalil Muqdad and Saeed Mirza Mahroos, and the Sunni head of the secular Waed group, Ibrahim Sharif - all demanded that they be freed.

There is growing instability on the Syrian side of the armistice line on the Golan Heights, Israeli chief of staff Lieutenant General Benny Gantz told MPs on Tuesday.

"In the Golan Heights, there is an instability developing that is on the rise, as a result of events in Syria, including in the zone adjacent to the border," Gantz told the parliamentary committee on foreign affairs and defense.

Palestinians on Tuesday staged small demonstrations to mark the 45th anniversary of the Six Day War in which Israel seized the West Bank and Gaza Strip.

Near the West Bank city of Ramallah, around 200 people protested by the Ofer military prison, with clashes breaking out as demonstrators threw stones at troops who fired tear gas.

Syria remains committed to the peace plan brokered by U.N.-Arab League envoy Kofi Annan, Deputy Foreign Minister Faisal al-Maqdad said on Monday, following a meeting with the chief U.N. observer.

"We shall work for the success of Annan plan," Maqdad told reporters, adding that he discussed with Major General Robert Mood "the joint work that we need to carry out together after the full deployment" of the U.N.-backed truce observer mission in Syria.

Russia said on Tuesday it was prepared to see Syrian President Bashar Assad leave power in a negotiated solution to 15 months of bloodshed that has claimed more than 13,000 lives.

Deputy Foreign Minister Gennady Gatilov said a day after meeting mediator Kofi Annan in Geneva that Russia would back any peaceful settlement to the crisis as long as it did not involve the use of outside force.

Syrian authorities have agreed to give relief workers access to four key sites, the United Nations said on Tuesday following a meeting on scaling up humanitarian aid.

"We will have a presence in Homs, Idlib, Daraa and Deir Ezzor to start with," said John Ging, director of the coordination and response unit at the U.N. Office for the Coordination of Humanitarian Affairs (OCHA).

More than 2,000 Syrians fled to Turkey in the past three days, officials said Tuesday, pointing to an increase in refugee arrivals which had dipped following a peace plan in April.

The number of Syrian refugees in camps set up in southeastern Turkey reached 26,747 on Tuesday, up from 24,433 on Saturday, according to figures announced by Turkey's Disaster and Emergency Management Presidency (AFAD).

Syria's government declared on Tuesday that the ambassadors and staff of several Western countries as well as Turkey were personae non gratae.

"Some states recently informed heads of our diplomatic missions and embassy staff that they are unwelcome," the Foreign Ministry said in a statement, adding Syria was now designating the ambassadors of the United States, Britain, France and Turkey, among others, as personae non gratae.

A U.S. State Department team will visit Moscow this week to discuss the Syria crisis, a top official said Tuesday as Western pressure mounted on Russia to back new action against its Soviet-era ally.

"We are in the process of meeting (U.S. Secretary of State) Hillary Clinton's deputies who work on the Middle East and Syria in particular," Russia's Deputy Foreign Minister Mikhail Bogdanov told the RIA Novosti state news agency.