Warplanes pounded rebel-held areas of Homs in the Syrian city's heaviest onslaught for months on Friday, monitors said, as Turkey reportedly returned cross-border shellfire for the second time this week.

The clashes came as the U.N. condemned the Syrian army's deadly shelling of a Turkish border town on Wednesday, and "terrorist" car bombs that killed almost 50 people in the war-torn country's second city Aleppo on the same day.

The United States said Thursday Turkey had taken "appropriate" and "proportional" action in firing back at Syria after a deadly cross-border shelling, but urged that tensions should not escalate.

"From our perspective, the response that Turkey made was appropriate," State Department spokeswoman Victoria Nuland said, adding Ankara had long made it clear that it would respond to any violation of its territory.

Turkish Prime Minister Recep Tayyip Erdogan said Thursday his country has no intention of going to war with Syria, hours after the parliament in Ankara authorized possible cross-border attacks, as Damascus said it was not seeking "escalation."

"We have no intention of starting a war with Syria," Erdogan said at a press conference amid anger over Syrian shelling that killed five Turkish nationals in a town that borders Syria.

President Michel Suleiman on Thursday noted that Syria was not seeking to stir chaos in Lebanon, stressing that the weapons of non-state actors will be eventually removed, “whether they belong to Hizbullah or the Salafist forces.”

“Syria does not have the objective of stirring chaos in Lebanon as it is barely being able to tackle its own problems at the moment, and we have to prevent a spillover of the Syrian crisis into Lebanon through endorsing the stance of neutrality that was taken by the national dialogue commission,” Suleiman said during a meeting with Argentinean reporters in Buenos Aires.

Russian objections to a draft U.N. statement condemning Syria's deadly shelling of Turkey sent the Security Council back into consultations, diplomats said Thursday.

The draft had been expected to be approved by a "silence procedure" -- the text is considered adopted if no country objects -- but "the Russians broke the silence," Britain ambassador Mark Lyall Grant told reporters.

Turkey's parliament on Thursday authorized military action against Syria but insisted it was not a war mandate following deadly cross-border fire that sent tensions soaring.

The vote came as Turkey retaliated for the shelling that killed five Turkish nationals, and Syria apologized and vowed it would not happen again.

Syria's chief ally Iran on Thursday urged Syria and Turkey to both show "restraint" following a border shelling exchange that threatened a broader conflict, according to the Fars news agency.

"The Islamic Republic of Iran asks both sides to show restraint, to investigate the issue and take note of the enemy's goals in the region," Iran's deputy foreign minister for Arab affairs, Hossein Amir Adbolahian, told the news agency.

U.S. Ambassador to Lebanon Maura Connelly expressed on Thursday her country's “grave concern” over Syria continued shelling of and incursions into Lebanon’s border region, said the U.S. Embassy in a statement.

She stressed to Prime Minister Najib Miqati “the United States’ expectation that the Syrian regime respect the sovereignty and territorial integrity of Lebanon.”

France on Thursday said a Syrian attack on Turkey which killed five civilians was a serious threat to global security and peace and called for an immediate halt to such strikes.

"This violation of international law constitutes a serious threat to global security and peace," Foreign Minister Laurent Fabius said in a statement.

Russia on Thursday voiced concern at the "deteriorating" situation between Syria and Turkey, where cross-border shelling has heightened tensions.

Turkey resumed fire on Syrian positions on Thursday, reportedly killing several soldiers, in revenge for mortar fire on Wednesday which killed five Turkish civilians.