Government warplanes bombed a town in northern Syria on Monday, killing at least 19 people, activists said, while the new U.N. envoy to the country acknowledged that brokering an end to the nation's civil war will be a "very, very difficult" task.

The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees said the airstrikes targeted a residential area in the northern town of al-Bab, about 20 miles from the Turkish border. The Observatory said 19 people were killed in the air raid; the LCC put the death toll at 25.

An amateur video posted online showed men frantically searching for bodies in the rubble of a white building smashed into a pile of debris. The authenticity of the video could not be independently verified.

Syrian's uprising began in March 2011 with largely peaceful protests against President Bashar Assad's regime, but has since morphed into a civil war in the face of a brutal government crackdown. Activists say at least 23,000 people have been killed so far.

The violence has escalated in recent months, and activist groups said Sunday that some 5,000 people were killed in August alone — the highest ever reported in more than 17 months of bloodshed.

Syrian officials said a bomb attached to a taxi blew up Monday in the Damascus suburb of Jaramana, killing five people and wounding 23. The officials spoke on condition of anonymity because they were not authorized to brief the media.

Activists, meanwhile, reported scattered violence in regions across the country, including the capital's suburbs, the region of Deir el-Zour in the east, Daraa in the south and Idlib and Aleppo in the north.

The LCC and the Observatory said more than 100 people were killed Monday.

Diplomatic efforts, including a six-point peace plan by former U.N. Secretary-General Kofi Annan, to solve the seemingly intractable conflict have failed so far.

Annan quit his post as special U.N. envoy, and was replaced Saturday by Lakhdar Brahimi, a 78-year-old former Algerian diplomat.

Brahimi, who also served as a U.N. envoy to Afghanistan and Iraq, commended Annan on his work, saying he did "everything possible."

"We discussed this several times and I can't think of anything that I would have done differently from him," Brahimi told the BBC in an interview. "It is definitely a very, very difficult mission."

He added that he is "scared of the weight of the responsibility" and that he is "standing in front of a brick wall. … We'll have to see if we can go around that wall."

Asked whether his task was "Mission Impossible," Brahimi said: "I suppose it is."

In Damascus, Information Minister Omran al-Zoebi vowed that Syria will lend the new U.N. envoy "every possible assistance. We will give him maximum assistance the way we did with Kofi Annan."

The Assad regime made similar public statements when it signed on to Annan's peace plan, only to frequently ignore or outright violate its commitments, failing to pull its troops out of cities and cease its shelling of opposition areas.

Al-Zoebi also sought to shift some of the responsibility for the future success or failure of Brahimi's mission onto the shoulders of Turkey, Saudi Arabia and Qatar — three of the harshest critics of the Syrian regime and strong supporters of the rebels trying to overthrow Assad.
The three countries, al-Zoebi said, must "stop sending weapons (to rebels) and close training bases," they are hosting.

The Syrian minister did not confirm or deny whether Syrian authorities are holding foreign journalists who entered the country illegally, but said that any person who does so, whether a Syrian or a foreigner, will be referred to judicial authorities.

He reassured reporters, however, that if any journalists are held by authorities "they will receive special treatment even though they violated Syrian laws." He asked journalists at Monday's news conference to give his office any names they have of reporters that they know with certainty are held by authorities.

At least three journalists are missing in Syria and are believed to be held by the regime.

Alhurra TV correspondent Bashar Fahmi, a Jordanian citizen of Palestinian origin, and his Turkish cameraman, Cuneyt Unal, are said to have been captured in the city of Aleppo after entering Syria last month. The third journalist, American Austin Tice, has reported on the conflict for The Washington Post, McClatchy Newspapers and other media outlets, is also reported missing in Syria.

Al-Zoebi also warned against foreign power intervening in Syria, saying "if anyone infringes on our national sovereignty there will be no red lights to our retaliation. … We will cut such a hand and make them pay a high price."

The West has shown little appetite to intervene in Syria in part because unlike the military intervention that helped bring down Moammar Gadhafi in Libya, the Syrian conflict has the potential to quickly escalate. Damascus has a web of allegiances to powerful forces including Shiite powerhouse Iran and Lebanon's Hezbollah and there are concerns that a military campaign could pull them into a wider conflagration.

Western powers, however, have warned Assad against using chemical weapons in the conflict.
On Monday, French Foreign Minister Laurent Fabius said that if Syria uses such weapons, "our response … would be massive and blistering."

Speaking to RMC radio, he said Western countries are monitoring the movement of the weapons in Syria to be ready to "step in" immediately. Fabius said "we are discussing this notably with our American and English partners."

Al-Zoebi also claimed some of the attacks against individuals and institutions in Syria "had the fingerprints of intelligence services, including Israel's Mossad." He did not elaborate or say which attacks they were allegedly behind.

Also Monday, Bahrain said it plans to fund a "mobile school" for up to 4,000 Syrian refugee children at a camp in Jordan. The school will be run by the U.N's Children's Fund, the announcement said.