U.S. Secretary of State John Kerry on Monday launched his first trip abroad since taking office this month by sharply criticizing the Syrian military's indiscriminate killing of innocent civilians" and renewing Washington's call for an end to Bashar Assad's dictatorship.

The recent new round of military backed-violence in Syria's second-biggest city was evidence enough that "Assad must step down," Kerry told a joint press conference with British Foreign Secretary William Hague in London.

Kerry also urged Syria's opposition to attend a planned international meeting in Rome this week, which the opposition pulled out of in protest at the international community's silence on the continuing bloodshed. Kerry was speaking after he held talks with British Prime Minister David Cameron at the start of an 11-day, nine-nation trip through Europe and the Middle East, which officials in Washington have dubbed "a listening tour."

"This is no accident that this is the first stop of my trip as secretary of state," Kerry said, stressing the strong partnership between London and Washington.  Cameron and Kerry used their meeting in Downing Street to discuss plans for a free trade agreement between the US and Europe. However, Kerry declined to comment at the press conference on next month's referendum on whether the inhabitants of the Falkland Islands will remain British.

Kerry insisted that an Iran with nuclear weapons was unacceptable. Both Kerry and Hague also discussed the situation in Mali. Hague stepped up his call for efforts to kick-start peace talks between the Israelis and the Palestinians. "There is no more urgent foreign policy priority in 2013 than restarting negotiations between Israelis and Palestinians," he said.   After London, Kerry is to hold talks in Berlin on Tuesday with Chancellor Angela Merkel and Foreign Minister Guido Westerwelle before flying on to Paris and Rome.

On Tuesday in Berlin, Kerry was to meet for the first time with Russian Foreign Minister Sergei Lavrov. Relations between Washington and Moscow have been strained recently after the Kremlin blocked efforts in the United Nations to take further action on Syria. Moscow has also banned US adoptions of Russian children amid criticism from Washington about Russia's human rights record.

Kerry's trip will also take him to the Middle East and North Africa, where his talks are expected to focus on the political crisis in Egypt. His visit represents the first occasion that Washington's key allies get to see how Kerry intends to approach his new job as the US' top diplomat, as well as the foreign policy priorities of President Barack Obama's second term. Kerry's predecessor, Hillary Rodham Clinton, visited a record number of countries as secretary of state during Obama's first term. Obama won a second term in November and was sworn into office in January.