BEIRUT, Lebanon — Seven of Syria’s most powerful rebel groups said that they had forged a new Islamic force seeking to topple the government of President Bashar al-Assad and replace it with an Islamic state.

The new alliance, the Islamic Front, was announced in a video shown on Al Jazeera television on Friday and featured some of Syria’s most widely recognized rebel commanders.

While some rebels and opposition activists hailed the new group’s formation as a major step forward for the anti-Assad insurgency, it remained unclear to what extent the announcement reflected a true reorganization of rebel forces or what difference it would make in practice.

Most of the participating groups, while maintaining their own command structures, have long cooperated in battle. And through two and a half years of civil war, new rebel formations have been announced frequently, many of them faring no better against government forces than those they preceded.