Yemen’s Iran-aligned Al Houthi militants have stepped up their attacks inside the port city of Hodeida despite a UN-brokered truce deal there, government forces have reported.

The extremists on Tuesday attacked government troops in several parts of the Red Sea coast city, using heavy artillery and mortars, a media centre for the pro-government Giants Force, said in a statement.

“The militias fired a number of artillery shells towards positions of joint forces in an escalation and violation of the UN truce,” a field military source said, according to Dubai-based television Al Arabia. No casualty figures were reported.

The latest escalation comes as UN peace envoy Martin Griffiths is currently in Yemen’s militant-controlled capital Sana’a for a two-day visit expected to focus on pushing forward the implementation of the faltering Hodeida pact.

Last December, the Yemeni government and Al Houthis reached an agreement in Sweden for redeployment and withdrawal from Hodeida.

At the time, the accord was seen as a breakthrough to end Yemen’s years-long war. However, its implementation has since been stymied over Al Houthis’ recalcitrance.

The militants still control parts of Hodeida, which is strategically important because of its key port through which most Yemen’s imports and aid enter.

Yemen’s conflict erupted after Al Houthis unseated the internationally recognised government of President Abd Rabbo Mansour Hadi and overran parts of the country, including the capital Sana’a, in late 2014.

In 2015, the Arab alliance led by the UAE and Saudi Arabia, intervened in Yemen in response to a request from the Hadi government after Al Houthis advanced on the southern city of Aden, the country’s provisional capital.