Adds analyst comment and dateline, updates prices

By Eric Onstad

LONDON, May 29 (Reuters) - Copper prices edged lower on Friday as investors waited for more news about a potential deal to extend a ceasefire in Iran and as the dollar firmed.

Three-month copper CMCU3 on the London Metal Exchange was down 0.1% at $13,690 a metric ton by 0910 GMT after gaining 1.3% in the previous session.

LME copper rebounded on Thursday on the back of news that the U.S. and Iran reached an agreement to extend their ceasefire and lift restrictions on shipping through the Strait of Hormuz.

But President Donald Trump has yet to approve it and Iranian state media said it had not been finalized.

"Copper is drifting lower today, it seems like we've got some profit-taking. We've certainly had a small uptrend for the last two weeks, but it's stalling a bit," said Ole Hansen, head of commodity strategy at Saxo Bank in Copenhagen.

LME copper is on track to gain 5.3% this month, largely on hopes for a deal to end the Iran war and signs of firmer demand.

The most-traded copper contract SCFcv1 on the Shanghai Futures Exchange added 0.8% to 104,840 yuan a ton. The contract has gained about 3% so far this month.

Both contracts were up for the second straight month.

"A successful deal could open the door for stronger gains, while any breakdown risks reigniting inflationary pressures and capping upside," said Tim Waterer, chief market analyst at KCM Trade.

Copper was also supported by the continued flow of metal to the U.S. as traders took advantage of a slight premium of U.S. futures over those in London.

U.S. Comex copper futures HGc3 dipped 0.2% to $6.44 a lb, bringing the premium of Comex over LME copper to 3.7% or $511 a ton.

"If you take copper out of the market into the U.S. then that helps to tighten the overall global market, so it's difficult not to paint a picture of underpinned and supported prices going forward," Hansen said.

Among other metals, LME aluminium CMAL3 was little changed at $3,660 a ton, zinc CMZN3 added 0.3% to $3,563, lead CMPB3 rose 0.3% to $2,024, tin CMSN3 gained 0.4% to $55,300, and nickel CMNI3 dipped 0.1% to $19,090.