Turkish Prime Minister Tayyip Erdogan said it would be up to the UN Security Council to decide whether to establish a no-fly zone inside Syria and said he backed the involvement of Russia and China in planned peace talks.

Speaking at the Brookings Institution in Washington a day after discussing Syria with President Barack Obama, Erdogan said a no-fly zone could be discussed at a planned international conference on Syria backed by Washington and Moscow.

Turkey, a US Nato ally, has been one of Syrian President Bashar al-Assad's fiercest critics, throwing its weight behind the uprising against him, allowing the rebels to organize on its soil and sheltering 400,000 refugees.

But Erdogan has grown frustrated by a lack of international consensus on how to respond to the violence. Car bombs, which tore through a Turkish border town last weekend in the deadliest spillover of violence yet, have added to the sense of urgency.

"With respect to a no-fly zone ... it is not a decision that could be taken between the US and Turkey. It is something that would have to come through the UN Security Council," Erdogan said.

"We are in the process of putting together a conference in Geneva ... If that process decides on such a zone, as Turkey, we would also do whatever is necessary," he said.

During his visit to Washington this week, Erdogan had been expected to push Obama, at least in private, for more assertive action on Syria.

Obama - who has been reluctant to arm Syrian rebels or become enmeshed militarily in the conflict - made no mention of deeper engagement during a joint news conference with Erdogan on Thursday, where the leaders sought to project a united front.

Western leaders have been cautious about the prospects of the planned talks in Geneva achieving any breakthrough, and Russia's desire that Iran should attend could complicate matters because of potential opposition from the West.

Iran is a US foe and the main regional ally of Assad's government, which has also received support from Russia. Tehran's desire to participate in a June 2012 meeting on Syria hosted by the United Nations in Geneva was a bone of contention between Washington and Moscow.

The main Syrian opposition, expected to decide its stance next week on the planned conference, has previously demanded Assad's exit before any talks, something Erdogan reinforced.

"President Obama talked yesterday about a process without Assad ... Having a transition with Assad in place cannot be a solution and the opposition wouldn't accept it in any case," Erdogan said.

Last year's Geneva talks brought together the foreign ministers of the U.N. Security Council's five permanent members - Russia, the United States, China, France and Britain - along with Turkey, Kuwait, Qatar, the Arab League and EU.

The new meeting will aim to include the same global powers, but this time would also have representatives of the Syrian government and opposition.

"A second Geneva process with Russia and China included has our support," Erdogan said.

He said he planned to travel to Moscow and to Gulf states to discuss the Syrian crisis after his visit to Washington.

Turkey has been among the strongest opponents of Assad but its enthusiasm for action against Syria has waned recently, partly in frustration at the fractured Syrian opposition and the growing brutality by both sides.

Erdogan has said Turkey, which has been testing blood samples from Syrian casualties for chemical weapons use, had shared its evidence with the United States, Britain and others and said Assad's forces had also fired several hundred missiles.

"According to Nato they have used 283 missiles, and according to other information they are using the chemical sarin," Erdogan said on Friday.

"These are issues that should be discussed in the U.N. Security Council and also perhaps in the U.N. General Assembly," he added.-Reuters