Embedding blocks into other blocks is not supported

Question

I have developed a Volt template and intend to use it as a default for others. There is an example of my code below:

{# LOCKED MODE #}
{% if session.get('locked_mode', true) is not empty and session.get('locked_mode', true) is true %}
    {{ partial('locked_mode_view') }}
{# UNLOCKED MODE #}
{% else %}
<div class="row">
    {{ partial('unlocked_mode_view') }}

    {% block content %}
        {{ partial('unlocked_mode_content') }}
    {% endblock %}
</div>
{% endif %}

While he was compiling, the compiler showed this error:

Embedding blocks into other blocks is not supported in...

I did not understand this mistake. What can I do in this situation?