Eritrea has rejected a new U.N. Security Council resolution that tightens sanctions against the country for supporting insurgents in Somalia.

A statement from Eritrea's Ministry of Foreign Affairs Tuesday said the resolution will heighten tensions and “stoke an already explosive situation in the Horn of Africa.”

On Monday, the Security Council voted 13-0 in favor of the resolution, with China and Russia abstaining.

The resolution condemns Eritrea for violating sanctions imposed in 2009 by continuing to assist Islamist militants in Somalia, including al-Shabab. It also allows the council to increase the number of people and entities that can face a travel ban and assets freeze.

Eritrea has denied assisting al-Shabab and other militant groups.

The foreign ministry blamed the new sanctions on U.S. hostility toward Eritrea. It said the sanctions are also aimed at protecting Ethiopia, a U.S. ally in the fight against terrorism.

The two East African nations are archrivals who fought a border war between 1998 and 2000.

On Monday, Ethiopian Prime Minister Meles Zenawi was among several East African leaders who asked the Security Council to toughen sanctions against Eritrea.

Eritrea was already subject to a U.N. arms embargo because of its alleged support for al-Shabab. That group is trying to overthrow Somalia's transitional government and set up an Islamic state.