A German rapper who converted to Islam and joined jihadist rebels fighting to overthrow President Bashar Assad has been injured in an air strike, a jihadist group said on Monday.

The jihadist, formerly known as Deso Dogg, was hiding at an anti-regime fighter's house that "was hit by an air strike and helicopter shelling", said a statement posted on Facebook by a group that identified itself as the People of Abraham.

At least 42 people have been killed in 10 days of clashes in Yemen between Sunni Islamists and Shiite rebels, tribal sources and an official said on Monday.

Tension is mounting with stumbling national reconciliation talks, begun after the ouster of former president Ali Abdullah Saleh last year, set to conclude this month.

Syrian President Bashar Assad warned Washington on Monday to brace for retaliation if U.S. forces attacked his war-torn country, as he denied using chemical weapons against his people.

"You're going to pay the price if you're not wise. There are going to be repercussions," Assad told CBS television's "This Morning."

Gunmen killed five policemen in a checkpoint shooting north of Baghdad on Monday, the deadliest of attacks that left 13 dead, officials said amid a nationwide surge in violence.

The unrest came days after an al-Qaida-linked group claimed responsibility for a spate of car bombings in the capital last week, killing 50, the latest in a spike in bloodshed that has raised fears Iraq is slipping back into all-out sectarian war.

Cyprus said Monday it had been informed that missile tests will be carried out by a "friendly" country in the eastern Mediterranean this week, as the U.S. weighs military strikes against Syria.

The tests come after Israel last week launched an Ankor (Sparrow) missile in the Mediterranean, ratcheting up the tension in a region already jittery over the possible fallout from any U.S.-led military intervention against Syria.

Tunisian security forces on Monday killed two Islamist militants from the extremist group Ansar al-Sharia and arrested two others in a Tunis suburb, the interior ministry said.

The two men arrested, Mohammed Khiari and Mohamed Aouadi, are leaders of the Salafist movement's military wing and are implicated in the assassination of opposition lawmakers Chokri Belaid and Mohammed Brahmi, a ministry source said.

U.S. Secretary of State John Kerry said Monday that Syrian President Bashar Assad could resolve the crisis surrounding his purported use of chemical weapons by turning "every single bit" of his arsenal over to the international community by the end of the week.

But Kerry, who joined British Foreign Secretary William Hague at a news conference in London, said he didn't expect Assad to do that.

The U.N. human rights chief said Monday there is little doubt that chemical weapons were used in Syria but she did not specify which of the combatants was suspected of using them.

U.N. High Commissioner for Human Rights Navi Pillay spoke two days ahead of the expected update from a U.N. panel probing for war crimes and other human rights abuses in Syria, including the use of chemical weapons. The 47-nation U.N. Human Rights Council, which authorized the probe, is likely to consider a resolution on Syria before the end of its session.

Foreign ministers of the Gulf monarchies will meet Tuesday in Saudi Arabia to discuss measures against Syria, as Washington drums up support for its plan to strike Damascus, a diplomat said.

Countries of the Gulf Cooperation Council "support taking international measures to deter the Syrian regime," the diplomat told Agence France Presse on Monday.

Syrian regime forces stormed a prison in central Homs province overnight to put down a riot by inmates, injuring several, the Syrian Observatory for Human Rights said on Monday.

"Several people were injured and there are reports that people were also killed when regime forces stormed Homs central prison," Observatory director Rami Abdel Rahman told AFP.