That would be a serious escalation, all the more worrisome because both countries possess nuclear weapons.

It is this period that witnessed the most serious escalation of violence.

This was the most serious escalation on the border since the 2006 Lebanon War.

This action led to a serious escalation in the confrontation between the traditionalists and the reformers.

Palestinian officials saw it as a serious escalation by the Israelis.

These incursions seemed to suggest a serious escalation in the conflict was imminent.

It would also mark a serious escalation in a covert war being fought by both sides.

The new crackdown clearly marked a serious escalation by the authorities.

There was a serious escalation in militant violence in 2004.

China will then be responsible for a serious military escalation that will ultimately lead to disaster.