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60 Minutes, AP Photo/CBSNews
In this frame grab from video provided by CBSNews/60 Minutes, in New York, "60 Minutes" contributor Charlie Rose, left, interviews Syrian President Bashar Assad, Thursday, March 26, 2015, in Damascus, Syria. Assad says he would be open to a dialogue with the United States, but that it must be "based on mutual respect," during the interview scheduled to be broadcast Sunday, March 29.

BEIRUT — Syrian President Bashar Assad has rejected allegations that his military used barrel bombs or chlorine gas against opposition-held areas, calling the accusations "malicious propaganda."

In an interview with CBS News, the Syrian leader also said that he would be open to a dialogue with the United States, but that it must be "based on mutual respect." CBS published excerpts of the interview online Friday.

The Syrian opposition and activists say government helicopters dropped bombs containing chlorine gas on the town of Sarmin in northwestern Syria's Idlib province on March 16, killing six people.

Videos posted online showed people struggling to breathe, and the international humanitarian organization Doctors Without Borders said symptoms described by medics in contact with the group clearly indicate the presence of chlorine poisoning.

Assad dismissed the accusations, saying "this is part of the malicious propaganda against Syria," and suggesting the rebels were behind the alleged chlorine attack.

"It's not used as military gas. That's very self-evident. Traditional arms is more important than chlorine, and if it was very effective, the terrorists would have used it on a larger scale," he said. The government refers to its opponents as "terrorists."

Also Friday, several rebel factions pressed their offensive on the government-held northwestern city of Idlib, capturing several outlying neighborhoods, according to the Britain-based Syrian Observatory for Human Rights. The group said 14 rebels and six troops were killed Friday, adding that many more from both sides are feared dead.

Syrian state TV said the air force carried out heavy raids on the outskirts of Idlib and nearby villages, killing "a number of terrorists." It said the armed forces are fighting "fierce battles" in the city of Idlib and its outskirts.

State TV said "thousands of terrorists are coming from Turkey to attack Idlib and its suburbs." Turkey is one of the main backers of the rebels.

Rebels and members of al-Qaida's branch in Syria, known as the Nusra Front, control large parts of Idlib province and have tried in the past to capture the provincial capital. The latest attempt appears to be the most serious so far.

The purported chlorine gas attack on Sarmin would be one of the most serious uses of poison gas in Syria since a deadly chemical attack outside Damascus in August 2013. In the fallout from that attack, Assad relinquished his chemical weapons program under a U.S.- and Russian-brokered deal, averting threatened American strikes.

But activists and rebels have accused the government since then of carrying out several chlorine attacks on opposition-held towns and villages over the past year.

The Organization for the Prohibition of Chemical Weapons has concluded "with a high degree of confidence" that chlorine was used on three rebel-held villages in Syria last year, killing 13 people. It did not assign blame. Last month, the OPCW condemned the use of chlorine in Syria as a breach of international law.

In the interview, Assad also addressed U.S. Secretary of State John Kerry's recent statement that Washington must eventually talk with Damascus to help negotiate an end to Syria's civil war.

In principle, Assad said, "every dialogue is a positive thing, and we are going to be open to any dialogue with anyone, including the United States." He said there is no direct communication so far with Washington.

"I would say what we have in Syria so far is only a statement, nothing concrete yet, no facts, no new reality regarding the political approach of the United States toward our situation, our problem, our conflict in Syria," Assad said.

Washington has long pushed for a negotiated political settlement to Syria's conflict, which has killed more than 220,000 people and wounded 1 million. The U.S. helped coax Assad's government and its opponents to the negotiating table early last year, but the talks collapsed after two rounds without making progress.

Since Syria's uprising began in March 2011, Assad's government has publicly supported international diplomatic efforts to ease or resolve the conflict, while simultaneously ignoring commitments it has made under brokered agreements.

In a separate interview with a group of Russian journalists, Assad lauded a Russian initiative to nurture talks between Syrian government representatives and the opposition in Moscow.

A first round of talks in Moscow in January made no headway. The main-Western backed opposition Syrian Nation Coalition shunned the meeting because it did not aim to remove Assad from power. The Coalition has said it will skip a second round of talks scheduled for next month.

"In order for this dialogue to succeed, it should be purely Syrian," Assad said, according to a transcript of the CBS interview published Friday by the SANA state news agency. "In other words, there shouldn't be any outside influence on the participants in this dialogue."

Russia is a close ally of Assad, and has provided diplomatic support and weaponry to help the Syrian leader maintain his grip on power. Moscow also maintains a small naval facility at the Syrian port of Tartous on the Mediterranean Sea.

Asked about his country's ties with Moscow and the possibility of turning the Tartous facility into a full-fledged Russian military base, Assad said he would "welcome any expansion of the Russian presence in the eastern Mediterranean and specifically on the Syrian shores and in Syrian ports."