Russia and the US have sent further warships to boost their military capacity in the Mediterannean as expectations grow of an imminent strike on Syria.
Syria's ally Russia is sending an anti-submarine ship and a missile cruiser to the Mediterranean, according to Russian news agency Interfax.
An armed forces source reportedly said the planned deployment was in response to the "well-known situation" - a clear reference to the conflict in Syria.
The navy has denied the deployment is linked to events in Syria, saying it is part of a planned rotation of its ships in the Mediterranean.
In the US, a defence official has said a fifth destroyer, the USS Stout, has been deployed to the Mediterranean and is "heading and moving east".
The guided missile destroyer is due to relieve the Mahan, but both ships might remain in place for the time being, the official said.
Other destroyers in the region - the Ramage, the Barry and the Gravely - criss-cross the Mediterranean and could launch their Tomahawk missiles toward Syria if so directed by US President Barack Obama.
As military action inched closer, Syrian President Bashar al Assad's forces removed several Scud missiles and dozens of launchers from a base north of Damascus, possibly to protect them from bombardment, opposition sources claimed.
The White House said it is on track to release an unclassified intelligence report on Syria this week, although the information is not a "slam-dunk" that will make an open and shut case for military action.
A spokesman added that what the US is contemplating in terms of its response is "very discrete and limited".
Russia and the US have taken part in an "urgent" meeting of the five permanent UN Security Council members in New York - the second such meeting in two days.
Russia is strongly against any military intervention in Syria, with Russian Foreign Minister Sergei Lavrov believing it would seriously destabilise the region.
Mr Lavrov has said any attack without UN Security Council approval would be a "crude violation" of international law.
Russia's President Vladimir Putin has spoken to German leader Angela Merkel by phone, with the pair agreeing the Syrian conflict can be solved politically, the chancellor's spokesman said.
"The chancellor called on the Russian president to use negotiations in the UN Security Council for a quick, unanimous international reaction," he added.
Public opinion in Germany is overwhelmingly against military action in Syria, less than four weeks before an election in which Mrs Merkel hopes to win a third term.
The warship reports come after US President Barack Obama said the US had studied evidence and concluded that the Syrian government was behind the alleged attack.
Mr Obama said any strike would be to "send a shot across the bow" and give a "pretty strong signal that [Syria] better not do it again".
He added the US had not yet made a firm decision about how to respond, but that it could take action even without the backing of allies or the United Nations.
The president's national security adviser Susan Rice, intelligence director James Clapper, defence secretary Chuck Hagel and secretary of state John Kerry are to brief Congress on Syria later, according to Reuters.
Questions are said to remain about who actually controls some of Syria's chemical weapons and whether President Assad himself explicitly ordered the alleged attack.
Italian Prime Minister Enrico Letta told state radio that his country condemned the Assad regime but would not join any military operation without UN Security Council authorisation.
The Syrian leader was shown meeting Yemeni politicians on state television on Thursday.
It quoted President Assad as saying the country would defend itself in the face of any aggression.
A draft resolution by the UK on authorising a strike failed to win the approval of the UN Security Council on Wednesday as Russia reiterated its objections.
China has also entered the discussion and warned the West against any military action.
"China calls on all parties to exercise restraint and remain calm and to remain committed to the correct track of political solutions," Chinese Foreign Minister Wang Yi said.
British involvement in any strike will be debated today by politicians in the House of Commons .
Meanwhile, United Nations weapons inspectors set out on Thursday morning for the Damascus suburbs in a third day of investigations.
UN Secretary-General Ban Ki-moon has pleaded for all sides to hold off on any military strikes.
He said his inspection team would soon finish its investigation, leaving Syria on Friday and reporting their findings to him the following day.
Samples they have collected will go to labs around Europe for testing, AP reported.
Last week's alleged chemical attack is claimed to have killed 1,300 people.