More than 1.5 million Syrians have fled their conflict-ravaged homeland, the U.N.'s refugee agency said Friday, warning that the real figure could be even higher as the tally only reflected those who register with aid groups.

Dan McNorton, spokesman for the U.N. High Commissioner for Refugees, told reporters that close to 250,000 Syrians were being registered each month.

Turkey has arrested one of the major suspects in the twin car bombings that killed at least 51 people in a city near the Syrian border, the city's governor said on Friday.

"We captured one of the chief actors involved in the incident at 11:40 pm last night," said Celalettin Lekesiz, governor of southeastern Turkey's Hatay city where the bombs went off.

Egyptian police closed the Rafah border crossing with Gaza on Friday in protest at the kidnapping of colleagues in the Sinai peninsula, a security source and witnesses said.

Three policemen and four soldiers were abducted on Thursday by armed men who are demanding the release of a group of prisoners held at a police station in the North Sinai town of El-Arish, official media reported.

The bodies of two Iraqi Shiites killed fighting in neighboring Syria alongside President Bashar Assad's forces arrived home on Friday, providing more evidence that members of Iraq's Shiite majority have joined the war.

The bodies, in coffins wrapped in Iraqi flags, were brought to the southern city of Basra by four-wheel-drive vehicle, an Agence France Presse correspondent reported.

U.N. chief Ban Ki-moon and Russia agreed Friday that a peace conference on Syria should be held "as soon as possible" even as Moscow defied growing global pressure over its arms supplies to the Damascus regime.

Ban met Foreign Minister Sergei Lavrov ahead of talks later Friday with Russian President Vladimir Putin about an impending international meeting on Syria that should include representatives of the two warring parties for the first time.

The Tunisian government will decide by Saturday whether to allow or ban Salafists from holding their annual congress, the interior minister said on Friday, warning however "death threats" from radical Islamists will not be tolerated.

"The final decision will be taken today or tomorrow," Lotfi Ben Jeddou told Kalima radio.

The United States on Thursday blacklisted the leader of the militant Al-Nusra Front fighting the Syrian regime, as well as four top Syrian government officials, including the defense minister.

Al-Nusra's chief Abu Mohammed al-Jawlani was designated a global terrorist by the U.S. State Department, which said he had been tasked by al-Qaida in Iraq with installing Islamic sharia law across Syria.

Documents and torture equipment found in Syrian security buildings in rebel-held Raqa show detainees were tortured when President Bashar Assad's regime held sway over the city, Human Rights Watch said on Friday.

A team of researchers working for HRW toured Raqa in northern Syria in April, a month after the city fell into rebel hands, and found the incriminating evidence, the New York-based watchdog said in a statement.

Syrian rebels seized three U.N. peacekeepers in the Golan Heights in the third abduction in two months in the ceasefire zone between Syria and Israel, the U.N. said Thursday.

The abduction of the three observers came as the United Nations struggles to persuade the Philippines to keep its troops in the Golan force, which has been hit by growing fallout from the Syrian civil war.

A U.S. soldier convicted of killing five of his colleagues in Iraq in May 2009 was sentenced to life behind bars Thursday and dishonorably discharged.

Army Sergeant John Russell was convicted earlier this week over the murders at a clinic for soldiers suffering from war-related stress at Camp Liberty, the largest U.S. base in Iraq.