UITableView delete all rows at once

How is it possible to delete all rows from UITableView at once? Because when I reload table view with new data, I am still inserting new rows:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    CustomTableViewCell *cell = (CustomTableViewCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[CustomTableViewCell alloc] initWithFrame:CGRectZero] autorelease];
    }

    //... setting the new cell here ...

    return cell;
}

Thank you.