Obamacare customers could pay 18 percent more on average for their plans next year and have fewer insurers to choose from, a new analysis finds.

Proposed 2018 exchange premiums for the silver plan, the most popular of Obamacare's three metal plan tiers, are 18 percent higher than this year, according to an analysis from the healthcare research firm Avalere. The data is based on the eight states that have submitted early rate filings from insurers.

Avalere's analysis comes as Democrats and Republicans are trading barbs over who is to blame for high premiums and insurers defecting.

Avalere posits that both sides are to blame.

The firm notes that uncertainty around the future of Obamacare and the law's cost-sharing reduction payments to insurers are likely contributors to premium growth.

Democrats have charged that Republicans, specifically the Trump administration, are sabotaging the individual market, which includes Obamacare's exchanges and is used by people that don't have an insurance plan from their job. The Trump administration has not committed to paying the cost-sharing payments, which reimburse insurers for lowering copays and deductibles of low-income Obamacare customers.

But there are serious problems connected to Obamacare that are also contributors.

These include inadequate risk mitigation strategies, poor enrollment and declining plan participation, Avalere said.

Republicans have continually said that the premium hikes and insurer defections are due to Obamacare's own failings.

Avalere found that so far plan participation is declining but could change.

To date, 47 counties covering around 34,000 enrollees would have no participating insurer on their exchange, Avalere said.

It also found 41 percent of counties will have one insurer offering plans in 2018, up from 33 percent for this year.

Avalere did say that the uncertainty in the exchanges and pending repeal legislation could mean that insurer decisions may evolve over the summer and that "additional entries and exits likely."

Premium prices could also change, as insurers negotiate with state regulators and final rates due out this fall.

The House passed the American Health Care Act last month but the legislation that partially guts Obamacare has stalled in the Senate.

Insurers are coming up to a pivotal deadline to file plan submissions for 2018 on Wednesday for plans to be sold on healthcare.gov. The website is used by residents in 38 states and the District of Columbia to buy plans.