Try using element from WebPage itemtype (from: http://schema.org/WebPage, I know that You are using NewsArticle in this case, but I used Article for this example):
<div itemscope itemtype="http://schema.org/Article">
<span itemprop="name">How to Tie a Reef Knot</span>
by <span itemprop="author">John Doe</span>
This article has been tweeted 1203 times and contains 78 user comments.
<meta itemprop="interactionCount" content="UserTweets:1203" />
<meta itemprop="interactionCount" content="UserComments:78" />
</div>
<ul itemscope itemtype="http://schema.org/WebPage">
<li itemprop="relatedLink"><a href="related_news_1.html">Related News 1</a></li>
<li itemprop="relatedLink"><a href="related_news_2.html">Related News 2</a></li>
<li itemprop="relatedLink"><a href="related_news_3.html">Related News 3</a></li>
</ul>
Google Webmaster Tools sees it like this:

Alternatively You can do it like this:
<ul itemscope itemtype="http://schema.org/WebPage">
<li><a href="related_news_1.html" itemprop="relatedLink">Related News 1</a></li>
<li><a href="related_news_2.html" itemprop="relatedLink">Related News 2</a></li>
<li><a href="related_news_3.html" itemprop="relatedLink">Related News 3</a></li>
</ul>
And Google sees it like this then:
