The leader of Yemen's presidential council declared a state of emergency and cancelled a security pact with the United Arab Emirates on Tuesday after Abu Dhabi-backed separatists seized swathes of territory.
"The Joint Defence Agreement with the United Arab Emirates is hereby cancelled," a statement said, while a separate decree announced a 90-day state of emergency including a 72-hour air, sea and land blockade.
The announcements by Rashad al-Alimi, head of the Presidential Leadership Council, come after the Saudi-led coalition fighting in divided Yemen said it struck a UAE weapons shipment destined for the separatists.
The UAE-backed Southern Transitional Council (SCT) forces have swept through the south of Yemen this month, taking most of resource-rich Hadramawt province and swathes of neighbouring Mahrah.
Alimi ordered the SCT to hand over the territory to Saudi-backed forces, calling the separatists' advance an "unacceptable rebellion" in a televised address.
The confrontation risks tearing apart the already fractured Yemeni government, which has different factions backed by oil-rich Gulf powers Saudi Arabia and the UAE.
It also threatens slow-moving peace negotiations with the Iran-backed Houthi rebels, who ousted the government from the capital Sanaa in 2014, triggering a military intervention by the Saudi-led coalition.