U.S. President Barack Obama will send his diplomatic and defense chiefs to Capitol Hill Tuesday to intensify a fervent White House effort to win support for military strikes in Syria.

Secretary of State John Kerry and Defense Secretary Chuck Hagel will testify to the Senate Foreign Relations committee in what will be one of the most high profile political set pieces in Washington in weeks.

Nearly 90 rebels were killed near the Syrian capital over the past 48 hours, a watchdog said Monday, as fighting raged ahead of possible foreign military action against the regime.

At least 29 of those killed, among them non-Syrians, died in an army ambush Monday in Adra, northeast of Damascus, the Syrian Observatory for Human Rights said.

Israeli and Palestinian negotiators held another secret round of peace talks over the weekend, a Palestinian official said on Monday, adding that there had been "no breakthrough" so far.

"A round of talks was held on Saturday evening between the Israelis and Palestinians -- this is the fourth round," since they restarted more than a month ago, the official told Agence France Presse on condition of anonymity.

Syria made multiple attempts to buy equipment in Switzerland that could have been used to make weapons of mass destruction, but officials blocked the sales, Swiss authorities said Monday.

A total of 14 attempted purchases by Syria were turned down since 1998 by Switzerland's export-control watchdog, the State Secretariat for Economic Affairs, its spokeswoman Marie Avet said.

Russian authorities are planning to send a parliamentary delegation to the United States for talks with the Congress over Syria, in a move publicly endorsed Monday by President Vladimir Putin.

"The initiative is very timely and correct," Putin told speaker of Russia's upper house of parliament Valentina Matviyenko and speaker of the lower house of parliament Sergei Naryshkin.

Britain's government said on Monday it had no plans to hold another parliamentary vote on Syria air strikes after last week's defeat but might revisit the issue if circumstances changed "very significantly".

Prime Minister David Cameron lost a House of Commons ballot on Thursday on taking action to punish Syria for alleged chemical weapons use, and had appeared to rule out any further vote.

A top Vatican official on Monday warned the war in Syria could escalate into a global conflict, a day after Pope Francis made an impassioned call for peace.

"The Syria conflict has all the ingredients to explode into a war of global dimensions," Monsignor Mario Toso, head of the Vatican's Pontifical Council for Justice and Peace, told Vatican radio.

Attacks in Baghdad and mostly Sunni areas of Iraq killed 17 people Monday, including eight in a coordinated attack on the home of an anti-Qaeda militia chief, officials said.

The Turkish consul to the northern city of Mosul and a top criminal judge in executed dictator Saddam Hussein's home town were also caught in bomb attacks.

An opposition group tolerated in Damascus on Monday accused the regime of responsibility for an alleged chemical weapons attack outside the Syrian capital but spoke out against any punitive strike.

"The use of chemical weapons against civilians is a key turning point in the bloody conflict," the National Coordination Committee for Democratic Change said in a statement.

NATO head Anders Fogh Rasmussen said Monday he is "personally convinced" that Syrian President Bashar Assad used chemical weapons near Damascus last month.

"Personally, I am not only convinced that a chemical attack has taken place ... I am also convinced that the Syrian regime is responsible," Rasmussen said when asked if he had seen intelligence to prove Assad was behind the suspected attack which left hundreds dead.