The number of protesters on the streets may have hit record levels, but Syria's opposition movement is struggling to forge a united front, frustrated by deep divisions over tactics as much as by organisational chaos.

Opponents of the regime of President Bashar al-Assad agree he and his security chiefs have to go, but they have been unable to coalesce around a platform, despite at least five meetings and the formation of no fewer than four separate committees in Syria, Turkey and France.

In the latest move, some 350 opposition members in Istanbul elected a 25-member National Salvation Council on Saturday, but plans to appoint a shadow government were thwarted after a simultaneous meeting in Damascus failed to go ahead after being attacked by loyalists to the regime.

"It is impossible to form a shadow government from here, without the full participation of the people inside Syria. That is not what we want," said Omar al-Muqdad at the Istanbul meeting.

Analysts warn that Syria could be heading towards a stalemate similar to that of Yemen, where initiatives to form a solid opposition have also struggled. "The movement needs a boost, and an organised face to attract more people could do that," said one analyst in Damascus, who asked for anonymity.

The last serious effort to organise an opposition was in 2005, when the Damascus Declaration grouping brought together secular intellectuals, Kurds and Islamists. Many were subsequently imprisoned.

Today's opposition, facing an unprecedented outbreak of dissent and struggling to keep up with events on the street, is riven by divisions – between dissidents in Syria and in exile, young and old. Growing frustration spilled over in Istanbul. "How many thousand people more will have to die before we will finally act?" shouted one man, to thunderous applause.

"Sometimes the Ba'ath party has as good a vision as some of its opponents," said Massoud Akko, a Kurdish writer and dissident in exile in Norway. "It is very difficult to create a united front as there are too many differences between us and not enough trust."

He pointed to the Kurdish groups, who have the most structured opposition through numerous illegal but active parties in north-east Syria, but are split among themselves and others. A group of Kurds left the conference after asking the congress to agree to more regional autonomy and claiming they had been marginalised.

Opposition members, who argue that differences of opinion are healthy, admit that an inability to unite is harming the movement, as Syrians look for a political alternative after four months of protests which have left more than 1,500 people dead.

"I hate the current regime, but I need to see a credible alternative," said one young professional in Damascus. "By what mechanism does the opposition think it will topple Assad? What will they do in terms of policy afterwards? It is all too vague so far."

The atmosphere in Damascus was similarly disappointing. "There are no plans to hold another meeting soon because there is too much resistance from the street and within the opposition," said one of the members due to attend the Damascus meeting on Saturday which would have connected to Istanbul via Skype. "I am worried the protests will turn more violent without guidance."

There have been increased reports of protesters fighting back in the face of security and army forces who continue to carry out raids. Many were arrested in the resort town of Zabadani close to Lebanon, while troops surrounded Abu Kamal on the border with Iraq on Sunday, activists said, after defections in the east were reported by residents.

Ali al-Abdullah, a writer who was released from four years of prison and who underwent heart surgery three weeks ago, was re-arrested from his house in Qatana, close to Damascus, where checkpoints have been set up.

The government's attempts at conferences have exposed similar divisions within the regime. A "national dialogue" last weekend which went ahead despite being boycotted by the opposition was extended after divisions between reformers and hardliners over the final statement.

Nour Ali is a pseudonym for a Damascus-based journalist