The United States on Wednesday warned of new international measures to halt Syria's bloody crackdown on protests after reports that more than 200 people had been "massacred" in two days.

The White House said if Damascus did not fully implement an Arab League plan to contain the violence, "the international community will take additional steps to pressure the Assad regime to stop its crackdown."

Human Rights Watch urged Jordan's Prime Minister Awn Khaswaneh on Wednesday to probe the death in custody of a 20-year-old Jordanian man, who allegedly helped two Syrians buy arms.

It called for an "independent inquiry into the death of Najem Zuhbi ... when in detention at the military intelligence offices in Amman, on November 16, 2011," in a letter to the prime minister.

Five Iranian technicians working on a power plant project in Syria were abducted on Tuesday by an unidentified group of people, the Iranian embassy in Damascus said Thursday.

Earlier, Iran's Mehr news agency said the kidnap took place on Wednesday.

France denounced Wednesday what it said was the "unprecedented massacre" of 120 people by Syrian forces and urged Russia to accelerate talks for a U.N. Security Council resolution on the crisis.

At his regular briefing, French foreign ministry spokesman Bernard Valero said: "Everything must be put in motion to end this murderous spiral into which Bashar Assad is dragging his people, deeper each day."

A Syria correspondent for Lebanese daily As Safir, considered supportive of Bashar Assad's regime was detained in Damascus, an editor at the newspaper told Agence France Presse on Wednesday.

"We lost contact with our correspondent Ahmed Dahnoun yesterday (Tuesday) during a protest at Midan Square in the Syrian capital," the editor said, requesting anonymity.

Former Prime Minister Saad Hariri stressed on Wednesday the need for the whole of Lebanon to come under the control of the state and army.

He said: “No one in Lebanon can eliminate the other and we are all Lebanese and bound to work together.”

Lebanon decided to join a team of observers to monitor a plan aimed at ending a nine-month revolt against Syrian President Bashar Assad’s regime in response to a request by Arab League chief Nabil al-Arabi, An Nahar newspaper reported on Wednesday.

Foreign Minister Adnan Mansour received a written request from al-Arabi inviting Lebanon to join the observer mission, the daily said.

The opposition Syrian National Council on Wednesday urged the U.N. Security Council and Arab League to hold emergency meetings after "massacres" carried out by regime forces.

Reacting to reports this week of the killing of hundreds of civilians, the opposition bloc called for an "emergency U.N. Security Council session to discuss the regime’s massacres in Zawiyah Mountain, Idlib, and Homs, in particular."

The Syrian navy and air force conducted live-fire man oeuvres on Tuesday to test their preparedness to repulse "any aggression against the homeland," the official SANA news agency reported.

"The air force and air defenses conducted maneuvers with live ammunition ... with a view to testing the combat capabilities of the air forces and to test their readiness to respond to any aggression" against the country, SANA said.

Defense Minister Fayez Ghosn on Tuesday warned that al-Qaida members have entered the country through the Bekaa border town of Arsal “under the guise of being members of the Syrian opposition,” noting that he will raise the issue in cabinet.

During a meeting at his office with a delegation of high-ranking Lebanese army officers, Ghosn said: “We have information that certain operations are taking place at some illegal border crossings, especially in Arsal, where weapons and some al-Qaida terrorist elements are entering (the country) under the guise of being members of the Syrian opposition.”