Aden (Yemen), Apr 7 (IANS): UN Special Envoy for Yemen, Hans Grundberg has said the presence of hostile military activities near the country's oil-rich province of Marib sparks concerns on the fifth day of the two-month ceasefire.

In a statement, the UN envoy on Wednesday briefed on the status of the truce that went into effect on April 2, pointing out that he has seen a "significant reduction of violence" but he noted there are reports of some hostile military activities, particularly around Marib.

Grundberg said the UN has set up a coordination mechanism with parties to maintain open channels of communication. However, he stressed that the UN is not responsible for monitoring the truce and it is "squarely" up to the warring parties in Yemen to uphold the ceasefire.

The envoy reiterated that this truce is an important but "fragile" step, urging the relevant parties to make the best of the truce and work to reach a lasting peace negotiation, Xinhua news agency reported.

The Yemeni government and Houthi militia have been exchanging accusations of breaching the ceasefire since it started.

Yemen has been mired in a civil war since late 2014, when the Iran-backed Houthi militia seized control of several northern provinces and forced the Saudi-backed Yemeni government of President Abd-Rabbu Mansour Hadi out of Sanaa.

The Saudi-led Arab coalition intervened on March 26, 2015, in the Yemeni civil war in an attempt to reinstate the government of President Hadi.

The war has killed tens of thousands of people, displaced 4 million, and pushed the country to the brink of starvation, according to the UN.